FWIW (I realize this is a fairly old thread) do not set power valve opening by looking at idle vacuum. You need to set PV opening by cruise vacuum. Whatever cruise vacuum is, go 2 points lower. I have about 8 inches of vacuum at idle and I run a 10.5 PV. That's because I have about 14-15 inches of vacuum at a cruise.
If you do it correctly, you can size the t slot much smaller and not have tip in issues.
