My 340 is also high compression 10.2:1 but with eddy heads and running e85. My timing at 10 psi is 23 to 24. All the tuning was done on a dyno, adding more timing than this didn't make any more power in my case.
Other factors that may come in to play, my turbo is on the smaller end and probably makes higher EGT's. I am also at high altitude, so dynamic compression might be lower.