I have both the RV-8 and RV-14 payware. Of course the RV-14 is 5 out of 5. The RV-8, 4 out of 5. This RV-4 is 4.5 out of 5. 3 flap positions, moving map, look and feel of an RV-4 are all positives. Panel, switches and stick could use a little more love, however, still a fine piece of freeware. (Apply rudder on takeoff, don't use too much brake on landing.) Have fun.
Curious if you mean the RV-10 payware from SWS, or the RV-8 from Terrainy? That one was a sad situation. I paid for it but had to uninstall it as it broke the radios in other planes. Also very underpowered. But the great news is that SWS is getting close to finishing their own RV-8. It's my favorite RV so I'm very excited for it.
Long story made short...a couple mph is difficult to account for and you have to know which RW aircraft the MSFS aircraft was modeled after.