Yes, that's what's most ppl say about the C5.
I never tried a S7 before, but all I can say is my C5 hold very well the tune and it's not that difficult to tune.
But what I like most about it is the speed and the screaming sound
This engine pulls rpm like it will never end. Prolly one of the most rpm you can get off a .21 engine.
It's because it is a 11 port with exhaust bypass and as well because it's derivated from the C5 on-road engine.
It will blow a 8 port, has maybe a tad less low end than a WS7 but kill them both in pure speed.
And yes, it is not very fuel efficient, but I can get 8-9 minutes out of the oversized 180 cc Sav fuel tank.
Been very happy and lucky with it so far and my only grief would be the break-in that was the most difficult I ever had ( can you say TIGHT piston / sleeve fit LoL )
I would only replace it when the C6 oversized R&B engine will show-up.
Anyway, my opinion is that you can't go wrong with R&B, WS7 or C5, you'll be happy with both.
I'll reserve my judgment on the 8 port as I have read so many horror stories... but if you're lucky, I think it has an awesome price / perf ratio.
DFF