I just got to a point where I have the option of getting Improved Pistol I, II, and III. Should I buy Improved Pistol III and skip Improved Pistol I and II, or is there an advantage to having all three upgrades?

Each upgrade improves a different aspect of the pistol's performance, so I imagine that they do not, in fact, stack.

@kungfugrip: Well, yes, all three apply at the same time. You don't have to choose just one.

But no, getting Improved Pistol III will not automatically also grant you Improved Pistol I and II. It's a suggested order, but all 3 do different things, and you're free to research them out of order if you want one upgrade sooner than the others.

@BisonHero: Cool, thanks. That's the info I was looking for. I saw somewhere online (IGN, maybe) that all three upgrades improved the chance for a crit, so I was confused.