This is exactly my predicament, I regularly fly my awesome N5cTT with a YS56 and Hatori pipe on 30% nitro. I have about 12 gallons of stuff here, and I did not want to start buying 20% for a 105.
I have sat here a barely run in YS91srs (I think you guys in the US call it the YS91 3Ds?) with a matching Hatori pipe. So I guess I'll use that for now and then get a 105 during the year next year, and add the shim and run it on 30%.
I would rather buy the same fuel for both Helis, and the YS56 is on fire right now (well I hope not!!) on 30% Optifuel.