I dont care what bodywork you have, if you are running the big plastic CIK rear bumper, you will have a TON of drag. Switching to a metal tube rear bumper will give you a noticable gain above ~60mph.
Luckily I have the option of either bumper and have been running the tubular one. I have been looking at testing some different noses to see if any work better than others in the draft. OTK seems to be the only ones that work on that, and when you look at the size/shape of the noses it shows. They really try to cover/deflect over the front tires and driver’s feet.
I wouldn’t get too carried away comparing OTK bodywork. As soon as you touch someone with it they get dented in and likely become worse than any nose on the market as far as aerodynamics. No cik nose is going to direct the air over/around the driver so any differences between styles will be negligible IMO.