Still trying to map out a timing curve

I would leave the laptop hooked up and drive it up to the problem rpm's and see what the timing and rpm's are according to the MSD unit. You may be hitting your rpm limit for the burnout limiter, and I dont recall if you said you hooked that up or not. That may be an issue if the unit is expecting to see a circuit there and there isnt one. Try disabling the burnout limiter and see what happens...

You should be at full advance well before that rpm. Your motor would probably like to see full advance fairly quickly, like 2500 rpm's. You definitely want it fully advanced by your cruising rpm, and with your OD that may be the deciding factor.