lets revisit timing
The question i am asking is what effect will changing the total from 34 to 30 have on engine performance?
Probably 15-40 hp at peak depending on actual details (exhaust, intake, etc). Mid-range and part-throttle will depend wildly on your actual curve (how 'fat' it is in the middle, how low/high the all-in rpm is, etc) and is much harder to predict.
It would be most notable from 3500rpm and up, and can definitely be felt. Likely only matter on on-ramps, etc. 32-36 is a pretty safe range for most builds, but details matter once you're at 34+ (cam timing, actual measured compression, altitude, etc). If you want a 'set and forget' figure where you don't need to worry about gas, temperature, altitude, etc - 30-33 is a probably OK for a mostly street driven vehicle. I myself see no reason at all to run 32 or less. So I'd be at 33-35 deg.
There's an engine masters episode where they went from something like 10 degrees less than optimal, and then kept pushing the timing up. Even 2 degrees has measureable results until they were within 2 degrees of 'optimal'. I think they got about 6 degrees past that with ever-increasing power, but were pushing the limits. They discussed exactly what
@Mattax pointed out: dyno pulls are done cold, not in traffic, and not in a heat-soaked engine with cheap swill from the corner store..
