New Digital User, Pentax Question

Hey, I'm looking at buying my first digital. I'm mainly going to be using it for taking biking and kayaking so I'm looking at smaller cameras with a bit of zoom... I've been reading about the Pentax Optio s4i and s5i. The differences seem small but a couple raise my questions: You can set the exposure controls on both to auto or 4 different iso speeds. The s4i has speeds of 50.100,200,400 while the s5i has speeds of 80,100,200,400. Would the difference between the 50 and 80 speeds make much difference. And would the added pixels of the 5 make much difference. Most of my shots would be for email and/or 3x5,4x6 (lower resolution) but for some shots I would raise the resolution for the occasional 8x10...
Anybody got any opinions??? Thanks, Kevin

The difference between the pixel count will be minimal at enlargements up to 8x10, and the difference between ISO settings is also too small to really concern yourself with.