Rob, if you're using sensible fuel and not running overcompressed, there's one other suggestion I can offer. While I've never had any overheating issues with the 35, I can't say the same for the 19. Between us, a friend and I have 3 plain bearing 19s, a 19BR, and two 19TBRs. Of those, the 19BR and one of the plain bearing engines have been very prone to overheating, regardless of settings and fuel. I've been at my wits' end trying to solve this, and couldn't. My final throw of the dice was based on the fact that PAWs tend to have a very sloppy fit between the cylinder and the fin assembly. Some people are of the belief that oil is designed to fill the gap and thus transfer heat; I reckon that for proper heat transfer, it should just fit better in the first place. (The other thing to bear in mind is that the 19 and 35 are bored-out versions of the 15 and 29 respectively, and actually have less fin area despite having more capacity. Perhaps they are inherently more marginal for cooling?) What I did was pull off the fins off the 19BR and wrap a couple of layers of Alfoil round the cylinder, so that the fin assembly fit nice and snugly when I replaced it - the idea being to have a good proper metal-to-metal fit.
I flew this for the first time this morning. One flight was very slightly overcompressed (evidenced by slight slowing in manoeuvres); despite this, the setting never actually changed, and the engine didn't overheat. The second flight was fast and slightly lean. Once again, it held the setting perfectly and showed no signs of overheating. I'm not yet ready to believe that I've cracked the problem - it'll take quite a bit more flying yet, plus trying the same thing with the misbehaving 19DS - but it's looking promising.
The overheating symptoms I was experiencing were that the engine would initially have a good setting (even slightly undercompressed), but would load up after a few manoeuvres. Vertical and overhead 8s were particularly prone to causing this. The engine would sag and slow, and not pick up regardless of what the model was doing; generally I would land it and stop the engine to try and avoid damaging it. The cylinder head would be sizzling hot. Does any of that sound familiar?