Rock polish is a waste on steelix...unless you are VERY careful with that EV spread...with 30 base speed, it aint outrunning anything...but after 2 rock polishes, maybe 3, it has nice speed...though umbreon fails in 4th gen, if you can pass a trap to steelix against a poke far outmatched by it *coughphysicalsweepernotHeracrossorVirecough* then you can set up, and sweep away...or you can use it with taunt against annoyers and trappers and walls...and wam! But it is extremely tricky to set up.
Steelix@Leftovers
Impish
252 Def, 252 HP, 6 Att
~Explosion
~Rest/Roar/Toxic
~Rock Slide
~EQ
My good 'ol 3rd gen set. Rock Slide or explosion can be replaced if you need to replace one, but otherwise, pick one of the 3 in the 2nd slot depending on your needs. Good thing is that this works in 4th gen too...just be careful since steelix is very weak to mixed sweepers. Good thing about roar is that steelix goes last anyways...so yeah, it can work great if you'd rather not use gyro ball...
Steelix@Life Orb/Wide Lens
Adamant
252 attack, split HP and defense
~Screech
~Explosion/Stone Edge/Crunch
~EQ
~Taunt/Toxic
Here's another novelty...use either taunt or toxic to get the foe to want to switch...or someother move that encourages the foe to switch...something like confuse ray, though Steel doesnn't learn it. Then, the next turn, use screech, and the foe that comes in...well, its defense is lowered...and you better hope screech hits. Then, absorb a hit (or so you hope) and attack with EQ or another move, depending on the opponent...there's a good chance for a OHKO...so blast away!
Since steelix has options like stealth rock and all that, you should consider using those moves too...so yeah, the coolest wall eva! Steelix! BTW, the novelty sets are of high risk...