Ditto, I have been impressed with the low smooth idle of many engines designed for low nitro. The Irvine .53, for example, idles superbly with 5% nitro. It just kept idle slower and slower, and just when I thought it was going to quit, it idled slower still. Yet as soon as I goosed the throttle, it spooled up instantly. I tried 10% nitro for one tank and saw no difference in the way it ran. So why bother?

Like Dar, I run 5% exculsively, unless the particular engine wants more nitro. Even though I live in the Land of Cheap Nitro, I see no need to use more just because it's relatively cheap. More nitro still is more expensive. And the much lower stochiometric ratio of nitromethane compared to methanol means you will burn more fuel per flight, which may not be a big deal with a dinky .46, but a Moki 2.10 will see a substantial difference. I can see Dave Patrick's reasoning for modifying the Moki for lower CR, but I rarely hear the original Moki owner here in the USA complain about the way theirs ran. I think those new DPM 2.10 owners are in for a rude awakening after running it for a season on high nitro. The fuel bill sticker shock might just sent them scrambling to raise the CR back up.

Unless the engine in question runs poorly, backfires, pings with high compression ratio and all other efforts fail to correct it, keep it the high CR.