Quite high, good luck. S&R is quite selective in its internships, so if they called you back, then they are keen to hire you unless something goes wrong at the second internship. In any case, recent years have seen S&R hire more than 10/year, which was many times the 2-3 that were hired when I was graduating (around 7 years ago).

Congratulations! As far as I know, S&R is very selective, so it's really nice that you got a call back. Must be doing something right. However, S&R is relatively stingy in the PPO dept., they don't offer many PPOs, around three in a year (not confirmed), but you get the idea. So, the probability of a PPO is relatively less, but of course everything depends on your hard work and luck.

Best of luck!