I have a ringed ASP 91 series 3 - I think some older versions are ABC - this engine pulls a 14x6 in the high 9000s on 5% fuel. On a 13x6 the ASP sounds as if it is overrevving. I also have the MVVS 91 which is ABC. On the same prop the ASP pulls more revs. That is on all reasonable prop sizes.

Both these engines work well on 5% nitro or less. Neither respond well to small props: I think a 12x6 on an ASP91 would make a lot more noise than progress. I have had good results from both engines in 3D models using a 16x4 ASP at less than 9000rpm.