I am running a simaler engine,(ARC rod and weights,G-TEAM cam,...)minus the flywheel,and I try to stay below 6,000 rpms.
The motor feels like it has more,and its week point, compared to the opposed twins that I race against,is below 3500.
Oddly enough,that seems just about win the twins start to fall off(4.000 rpms)maybe that,and the stock flywheel is why Im a bit conservative.
If it helps at all,I run 7.5 revelutions moter,to 1 revolution rear tire.And this has worked out best for me at all 4 tracks that Ive raced at.But these are all left turn only tracks on a good hard smooth clay surface.