that is a good queston, i wonder also, i previoulsy had the pa50, and now i have the E60, and i like the sounds of it (drums are soo good!) but i still have the feeling pa50 did a little bit better. just my oppinion.
compared to pa500, i believe the difference would be even more noticeable.

anyway, E60 is still a great deal. you get 76 keys (be aware that the keys are different than E50, longer, nicer feel) you get great styles, good sounds, light weight, great build quality, beautifull design (i think is the best apart from "big boys" arrangers) nice OS and very good support and advice on www.roland-arranger.com, non-official roland forum.

if you need to buy without see, highly not reccomended, you need to listen to the demos vrey close and compare with whatever options you have. pa500 seems appealing, at about the same price, you need to balance very carefully what you get with either of these two keyboards.