I admit the builds are different was, thinking more along the lines of the final drive ratio. Without reading thru my thread from memory, the SA hub reaches a bit of over drive in third.. You really only need to figure the final ratio for top gear if that’s the one you will use. That’s the issue with so many speeds. If you are building a trail bike then the large gear range would be useful. Would be not much fun on the street, as it would involve a bunch of shifting or gear skipping. Not an issue with an IGH, but not ideal. I have built many bikes using the Nexus three speed. While somewhat fragile, they work fine with an auto clutch as the power is gradually applied. The fastest bike I built used a CAG 49cc and a Nexus 3spd. It’s ability to rev so high allowed a low ratio for pull away from stop, and to reach speed of 45+ turning close to 10k.
the SA fixie hub is robust enough to pedal start the CG engine. It also is a locker so there is engine braking versus free wheeling. I got a bit overboard on the final ratio on it and the bike is a bit faster in second than third as it a bit to heavily loaded to rev out. Still it’s a pleasure to ride.
Probably the cheapest thing you can do is change one of the 9t sprockets to a 10t or an 11t. With the 10t sprocket at 6800 rpm you'll have a mathematical speed of 37 mph in 8th gear. With the 11t you'll have a mathematical speed of 41 mph at 6800 rpm in 8th gear.
Realistically consider yourself very fortunate if you can move a total weight of 230 lbs at 37 mph on level ground using 1.6 max hp. Get a tachometer/ hour counter and bicycle computer so you'll know exactly what you're doing. You should be able to get both for less than $30 off eBay
I love the wider range of the 8 speed and also enjoy the act of shifting especially with all the work I have into it. I usually start in 2nd and if I'm riding to get somewhere I just use gears 2 , 4 , 6 and 8. If I'm pleasure cruising I still start in second (not really many hills around here) but I'll run most of the rest of the gears using the sound of the engine to tell me when to let off the gas shift then take off.... bbuur buurrrr bbbuuuuurrrrrrrr. My exhaust sounds so much better then I thought possible (not loud but has a Jazz Bass quality to it). I'll have to put up a video or a link to a video when I get a chance.