The reason Outrage Mix Mence isnt good against stall is because it RELIEVES the offensive pressure. It gives Forry and Skarm a chance to come in and spin away that SR, set their own Hazards up and do what ever they want. New Mixmence also loses 41% of its health JUST from attacking once (SS+LO+SR). That also puts you in Brave Bird range for Skarm...lol
I use Bold blissey
and Outrage doesnt come anywhere close to OHKOing (47.2% - 55.8% <-- 16 att neutral mixmence aka the new standard vs 252 def/0 hp Bold blissey and vs calm it does 51.6% - 60.8%, not exactly the end of the world bliss can still wall after this) so even if you predict correctly i still have like 90 other things that can take the weak Outrage after and then set up.
Really Classic Mixmence is 1000000x a better stall breaker than new mence is, mainly because it doesnt basically sign itself up to a death warrant by locking itself in and can Roost off SR damage so it can actually stick around.
Even DD Mence is a better stall breaker than New Mixmence is, mainly because of the new fad of Sp.Def Careful Forry (Relaxed Max sp.def is btw since it doesnt get 2hko'd by DD LO Outrage and CB Weavile Low Kick) who gets, as said, 2hko'd by that same DD LO Outrage. It also cant be revenged and doesnt nerf itself after attacking (-2 sp.att and/or locked into a WEAK rage).
New Mixmence is prolly better against bulky offense or maybe not but this thread is about what breaks stall so thats irrelevant.
But Outrage is a finishing move anyway. No one in their right mind is going to Outrage with Forretress and Skarmory around unless a really good opportunity presents itself. If you're playing vs. stall and it's new mixmence vs blissey and it comes in with 60% health from Draco + SR (common scenario, trust me), it's really not very difficult to catch the Skarm switch-in and kill it with a weakened but still potent Flamethrower. You're basically calling New MixMence horrible because it has Outrage, but that's actually optional to use and should only be used for mid game sweeping anyway. You seem to be locked into the mindset that every time Blissey comes into the battle Salamence has to Outrage, but that's not really how it works.
Also, don't really know who ran those calcs =\. Have a look:
310 Atk vs 130 Def & 714 HP (120 Base Power): 399 - 471 (55.88% - 65.97%)
Max/Max Blissey (which is less common than Calm) can't even take that hit. And in case you're wondering what it is against 0 HP/252 def calm bliss:
310 Atk vs 119 Def & 651 HP (120 Base Power): 436 - 514 (66.97% - 78.96%)
So no, Blissey isn't going to outstall Outrage unless you take a HUGE risk and Protect two straight times (AKA you suck at using stall teams).
This is in fact relevant to this thread since New MixMence has been for me very effective at breaking a stall team wide open once a Pokemon or two has died. At full strength, it can't do anything, but nothing can beat a stall team at full strength so I mean...that's not something you can really argue. It's also a great lure because of Outrage's weakness as I outlined above. I've caught a few Skarms coming in on it.
But your main point is that Outrage is easy to set up on. This is true for all teams, yet most everyone (including you iirc) agrees that Outrage is one of the best moves in the game despite that...and it is. In other words, I think you're overrating its downside. Yeah, two layers of Spikes sucks, but a lot of people Toxic Spikes proof their team, and by extension Spikes don't hurt many things except stuff that can't hurt stall much like Heatran and CB Scizor (assuming Blissey is played well). It's not like vs heavy offense where Gyarados comes in, gets a DD, and then just massacres you. You really CAN recover from Spikes pretty easily.
More importantly, A Skarmory setting up Spikes is also a Skarmory that is giving *insert sweeper here* a free switch-in. If you Whirlwind and stack up damage, more power to you (unless Salamence uses Flamethrower lol), but something is still coming in. And since MixMence shouldn't be trying to break stall early anyways, it will be much easier for holes to exploit since they should be there already.
Another thing: Blissey can be Pursuited, which essentially eliminates the NEED for Outrage (and really you never need it). Blissey is easy to bait with Explosion and everything else. Opening up Draco is very nifty. I've played about 4 or 5 semi-stall teams on the ladder (since I never ladder this is a lot for me), and every time I blow up Blissey with Gengar and then they're very vulnerable.
Lastly, it really bugged me that you said that Classic MixMence is better at breaking stall. It's really really terrible at it though since it doesn't pose a threat at all after a Draco Meteor. Unless it's using a weak unSTABed attack, it's basically attacking once and getting out quickly. Roost rarely helps since breaking stall isn't about surviving, it's about killing. Yeah, keeping your stall breaker around longer is good, but it still has trouble breaking common stall members like Tentacruel and Blissey. Maybe I was using it wrong or something, but Draco Meteor is basically the only thing going for Classic MixMence against stall teams. At least New MixMence actually has some versatility.
Conclusion: Yeah New MixMence sucks vs stall if you try to do too much with it and use it wrong, but um it's actually really good once it has room to work with. And every offensive stall breaker (aka things that aren't stuff like the Mismagius posted earlier) needs to have something batter the core a bit before it can have an impact. The same is true of New MixMence, and holding it to the standard of "well it should beat *insert solid defensive combo here*" is absurd and unreasonable.
Just because it has Outrage doesn't mean it's suddenly impotent against stall teams. After all, Outraging against a team with 2 healthy Steel-types and a Hippowdon is really stupid.
EDIT: and the point still stands that if Outrage KOes something that opens up a hole for a given sweeper, Spikes stacks don't matter a whole lot lol.