SSR2, SSR4, SRV4 (in warmer temps supposedly), SRV5. Really, you're looking at the 2010-2011 line, which is basically anything Easton made prior to trying to make something to supposedly hit the 52/300 better.
SRV4 is supposed to be fragile, but I took 75 cuts in 45 degree weather with the one I just obtained, about half were old 44/375s, and it didn't make any difference.
IMO, these bats hit the 52 just as well if you know how to hit. I have 52s for BP as well, haven't noticed much of a difference in distance if you're swinging up from the chest/waist area and putting spin on it.
The SSR4 I just sold was crushing both.