What are the recommended spark plugs for stage 2? I'm on Ruthenium's and am seeing some spark knock that I'd like to eliminate. The latest v2.51 tune file helped a bit (was seeing -4.5 / -3.5 on cyl 3 & 4 respectively), and I've now got a full tank of 91 + octane booster to see if I can get it down even further, but when my hybrid turbo + MPI kit gets here, I'd like to go 1-2 heat ranges colder so I'd like to know what to consider.