been running a 20x8 on my 41cc. taching in the 6500 range. switching to an 18x10 and reading 7500rpm. will be flying with this new setup in a day or two and wondering how much difference i'll have in performance?

The 18 x 10 will give you more speed but less acceleration on the takeoff run and less vertical performance than the 20 x 8.

Elson