4 or 6 degree shims?

I've got a 99 classic with an RE 2" BB and I do have some minor driveline vibration at 55-60mph. I have decided to upgrade to the RE 3.5" super flex kit and realize that I will need a SYE kit and new driveshaft, but I can't get it just yet. I'd like to lift first and see how she does before I invest another $350+. Since I already have the extended brake line and AAL bolts for the kit, the dealer has agreed to substitute RE shims. Anyone know which ones I should get? 4 or 6 degree? Anyone have experience with RE shims?

i got a RE 3.5" superflex kit, it gave me almost 5"of lift..i got it with the new spring packs....i put 4 degree shims in it solved my vibs pretty well

I used 6* shims with the 5.5 kit and a SYE.