Interesting reading. I started flying pattern in 1973 at age 15 with a Super Kaos .40 with a non-schnuerle ported OS 40. Progressed to a Kaos .40 with an OS .40FSR then a Super Kaos .60 with an OS .60FSR. The Kaos .60 had fixed gear and was all monokote - very light for the era - with the OS .60FSR it seemed like I'd never want more power.... I've flown 'current' pattern aircraft ever since. I still love the 'missiles' of the '75-'85 era (I have a Curare and an Arrow kit); even more I love the simplicity of .60 sized pattern ships. I have an MK Super VR-90 with a Hanno special with an APC 13x10 prop which can fly the current FAI sequences very nicely AND its cheap to operate and easy to transport!
As for the piped .60 versus the 4-stroke .90 issue in the SPA I think noise reduction reason is pretty logical and I'll bet there isn't any noise testing at the SPA contests. It's easy to get great performance from a 2-stroke .60/.61 without breaking the sound barrier - run more prop and a longer pipe. Keep the pitch up and you'll have loads of horizontal speed and vertical, too. I've run apc 12x10 and 11x11 on my OS .61VF with great success. Back around 1980 I had a Deception with a YS .60FR running a 10.5x7.5 zinger. LOTS of speed and LOTS of noise - I don't miss the noise!
I hope the SPA finds away to add an 'unlimited' type class with piped .60s (and retracts, too), but I think a noise restriction is an acceptable compromise. 93DBA at 25 feet is pretty easy to achieve (is that over grass or asphalt??)
Happy Flying,
Will B.