Sigma 14mm- f3.5 v. f2.8

Comparing these two lenses in situations that I would be in underwater, would they be equal at mid range apertures?

I realize viewfinder brightness, how big of a deal do you think this is on a D100?

I'm going to Key Largo, and would like to experiment with ambient light WA shots of the wrecks. How big of an advantage is 2.8?

Basically, I think I know I should spend more money, but as DS Monkey, I don't have lots to spend. All input is appreciated.

Buy the used 2.8 in the Wetpixel classified section. It's even less than any 3.5 that you will find anywhere...

[edit] Never mind, I just went back and checked and it's the 3.5 for sale... [/edit]

Cheers

James

These lenses can be quite big and bulky. Make sure that they fit in your ports before you buy.