TimmyB--
My 503t is the only track ball I still have in the bag; drilled a 716c, and 508a--- both were "okay" but didn't survive the yearly trade in for new stuff routine.
The 503t is stronger than average, and fits in below my Brunswick Nexus (original solid, drilled almost identical) but is a good 5 boards less overall. Basically, if I want a strong, semi-early rolling ball, but there's not enough oil for my Nexus to roll correctly, I go to the 503t.
Also, its the only ball I've had multiple 300's with... I average about 1 300 a year, but last year I had 2, within a month at different houses (one synthetic, one broken down wood).
I love the 503t-- match up the surface with your game/arsenal and enjoy. For me, oob plus a hand applied 2k pad really works well-- that's the level I take it back to every cleaning, and I've enjoyed the roll/hit since it came home with me.
To give you an idea of strength-- its about 5-7 less overall than my Nexus, but rolled very similarly to a like-drilled Victory Road solid (503 is more responsive off the spot) and its about 3 boards stronger than my Columbia Benchmark (same look overall, 503t is just more though).
Hope this helps-- buddies has them for like $70 shipped or something, well worth picking up another one for down the line.