Thanks Allan, that's a help. I picked up a set of 2-1/2" wheels today so experimenting with some 13x4" Props can happen after this weekends contest.
Since my last post I've flown the 61CXLS/Legacy with an APC 12.25 x 3.75 Prop - this wider chord Blade didn't seem to match well as the Engine wasn't happy with the <10,000 RPM needed to keep Air Speed manageable on the 66' lines.
Flew a couple of flights yesterday with the APC 12x4 narrow Blade Prop back on @ 10,000+ RPM launches - gives an effortless run with a strong 4 stroke. A 4" narrow Blade seems the ticket.