I thrive on the p/m --- so much i have 3 of them, just found one nib that i will keep for the future. about a benchmark ball, i think it depends on the bowler, how he/she throws it, and what type of drill pattern. again i start with this ball then ill change to something else after i get my read off the p/m's reaction. my opinion, p/m was the best "san antonio" track ball. to walter-- the p/m will react way different than your equation, not to sure on the s/i though, i dont have one of those. but i believe if you can get a p/m you better not pass it up, you will love it.