I have the v3 and recommend it for a 7 weight, its what I use and I think you would have a enough room for backing with an 8 weight for bass fishing. Bass don’t really take you into your backing anyways.
Less than 1/2 an ounce difference between those two reels. You won’t even notice the difference no matter which one you put on. Now…is that weight the proper weight reel with backing and line for THAT rod is a different question. But between those two reels…it doesn’t matter.
I’ve got a 3 on my 7wt, but as close as they are in weight, I think the issue will be less a matter of balance as line capacity. Depending on how much backing you think you need, the 3.5 might be a better choice if you upline. If backing isn’t an issue, the 3 would probably be okay in both cases.