I just started getting B-55 'cause I heard it better. So today I put it to the test. The bow used is a 54" recurve, 41# @ 28". I used only one arrow each time, 500 gr. 5/16" birch, 29" BOP. The B-50 string is several years old and has beed stretched about as far as can be, the B-55 string I just made today. Both are 10 strand, and the brace ht. was the same each time at 7 1/4". The both strings make about the same noise, very little, no silencers on either. I don't have a chrono-ma-jigger but I shot a block target and measured penetration. The B-55 String consistantly had 1/2" more penetration and at distance of 25 yrds consistantly had 1"-2" less drop. B-55 being brand new and the B-50 being broke-in I'd call the B-55 a better string. Costs less too, so a much better string.
So I use B-55 now.