As Hells Malice said, buttons on mice is pretty pointless. You're better off getting a Logitech G15 keyboard (only say that as it's what I have

) or something similar. It has 6 fully programmable keys on the left hand side and 3 modes for each key (there's 3 profile buttons above them) so in total that's 18 different keys/macros. More than you'll get on any mouse. Plus, these keys are FULLY customisable with the G15's software, you can assign them to do almost anything you want; timeable macros, other keys, blocks of text etc. and all of this can is changed automatically depending on what game / application you're in. Plus, it has an led screen that shows in-game stats amongst other things, bet you can't get that on a mouse.
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But having so many mouse buttons means less fiddling around with keyboard buttons that are hardly isolated at all from the others so there isn't much tactical advantage. I do not understand how people use WASD, I can't instantly find the keys naturally (unless you play by using your ring finger for W and D and your pinky for A.) I can instantly find any key surrounding the arrow keys on a keyboard. I would much rather have isolated buttons on the mouse
Seriously? First person I know.

After a few hours of gaming WASD become a natural resting position for your left hand and it's easy to find. I think your problem is you're using them wrong. For most people your ring finger goes on A, middle finger on W / S (never needed at the same time) and your index finger on D. You then have your little finger free for resting on shift and the middle part on your little finger for ctrl. Plus your thumb is free for space. Your index finger can also easily reach other keys such as E, R, F, G, V, C, X and T and I personally use my ring finger if I need to press Z. Not to mention there's also 5 number keys above all this within easy reach using any finger.
Then, on top off all of that, if you have a gaming keyboard such as the G15, you can quickly move your hand slightly and press any of the 6 fully customisable keys down the left hand side. And if that's not enough move your hand slightly further in order to switch between profiles for these 6 extra keys.
So, why give yourself hand cramps trying to grip, move and press awkwardly positioned buttons that are scattered all over a mouse at the same time? Mice are god for pointing, clicking and about 2-4 macros that need that tiny bit extra response time (in FPS games).
Edit: just counted and I have 40 keys at my disposal with just my left hand, which barely has to move an inch to reach the furthest ones. (and that's not even including the right hand side of the keyboard, just keys to the left of 5-T-G-V)