I didn't see it mentioned in the Q2 and Q1 discussion, but the Q1 had a set of drivers reversed. The Q1 was to the Q2 what the S1 was to the T1...the unique forerunner.
It is well worth noting that the Pennsy was AWOL from the early years of the superpower era, not entering the superpower era until 1939. The PRR's attention was focused on their electrifying projects during this time period. They then shifted from simple, plain jane power to exotic steam (which generally was a failure...despite being interesting). The Q2 was the best of the newer Pennsy steam, and they lasted less than a decade...with the J1s (a 1930 Lima/C&O designed 2-10-4) out living them (the T1s had short lives as well). Personally, I love the S1...talk about an awesome locomotive.