Wheel Question - 7/9 or 8/10?

I am planning on buying new lighter wheels (Jongbloeds) and I wanted to get the group's take on the advantages/disadvantages of 7s and 9s vs 8s and 10s. I have an Elan DP04 which is an FE front with a VanDiemen/Elan back. The FEs run 8s and 10s so that is the stock set up for the car. I very much like the way the car handles but as I am looking at new wheels I thought I'd take a harder look at size question. What is everyone using and why? Any reason not to use the 8s and 10's?

Doug