For a small wedding coming up, I was going to go with 8",6" and 4" tiers but not sure if that would look right with them being 2" different in sizes. Most wedding cake pics I have seen, the cake sizes seem larger than 2".

It depends. Sometimes it looks just right, sometimes a 3" difference is better. It comes down to how many servings are needed thuogh basically.

Depends on the look you are going for and the number of servings they need.

How many servings do they need?

Well, first she told me she only needed about 25 servings so I was thinking a two-tier. Then she said she wanted a three tier so I figured for the smallest amount of servings, I would do an 8". 6" and a 4". I don't want to keep adding to the number of servings and she doesn't want to pay for a dummy tier so I don't know what else to do to make it look bigger. Just wondering how the 8.6. and 4 would look for a wedding cake. I have done birthday cakes with those sizes but never a wedding cake.