Good questions on carrydown. First, just my own opinion based on experience, I don't think one bowler on a pair using urethane promotes much carrydown. I say this talking mainly about house shots. There is little or no oil outside 10 board to begin with, thus not much oil to carrydown. To the extent there is carrydown on a house shot it helps me if I am willing to not fight it, but rather use the mid lane hold area that is being set up, assuming there is any. Also, to the extent there is carrydown, the urethane balls themselves will be most susceptible to it. A big advantage of resin from the day one it was first introduced was its ability to cut through carrydown way more effectively than urethane.
I have an experience from 25 years ago when the resin ball was brand new and most
everyone was still throwing urethane. I was bowling a step ladder rolloff in a big money singles league and had just purchased an excaliber. We were bowling on a fresh pattern, and when I went to start practicing, waiting for my match, I started with my blue hammer playing about 7 board. Within 5 shots I went from flush strikes to flat 10's then to buckets and washouts while trying to move right to no avail. I got my excaliber out, and immediately went right back to 7 board getting a good reaction to the pocket. I then watched a series of matches where nobody but a lefty could crack 160. I took my excaliber into the championship match and won a close game with a low 200. Doubt if I could have cracked 180 with the urethane
As to the second question, I don't think there is much difference between the modern urethane and the old urethane, except that we routinely screened the old balls down to less than 600 grit. In addition the oil patterns were much shorter and the oil was lower viscosity then, making comparisons difficult.
