I agree with riku :/ it can be of their naturesThat's because of the nature of your Dialga and Palkia, if they both had one of the neutral natures then Palkia would be faster.
Determining if a Pokemon is faster or not isn't about opinions. >_> It's about the facts.No-one, lol im joking. Everyone is entitled to their own opinion and I think Dialga would be faster, and better :). Also it dpends on a few other things, so I guess they could both be quicker, depending on nature and drugs.
While we're on the topic of EV's, exactly how significant is EV training? Is there a huge difference in stats (like 100 to 150)? Or is it so small that it would only make a difference in competitive play (100 to 105)?
Each Pokemon can hold up to 255 EV's to a certain stat. Every 4 EV's translates to 1 point to that stat, thus a Pokemon can gain a maximum of 63 points to a stat.
While it may seem insignificant, it does matter a lot, especially with Speed. Going first can secure you victory if you can strike hard enough.
IVs have a more significant effect on Pokemon's stats than EVs though. ... well if I remember correctly at least.
That is considering that it's the new, fresh one and not the old, crappy one in R/B/Y(where you could max out your alakazams stats) right?
You also forgot to mention that they can only hold 510 EV's, so some EV's go to waste if it is maxed out.
Yeah, I'm going to tell you what everyone else said.
Natures, EV's, and IV's are what makes your dialga faster.
~Knowledge is power~