You're certainly doing a lot better than I am. Before tanking 2 48-question renal blocks, I was averaging 63%. Now, I think I'm at 58 or 59. However, I'm still in class and can't totally dedicate my efforts to board review, even though I'm trying to. I also just started doing this review strategy a couple weeks ago. In any event, I imagine that hitting in the mid 70's is excellent, particularly for this far from your test. I'm taking it June 21, for what it's worth.
Looks like I'm the low-ball in this group. I'm at 52% but I attribute that to my awful pharm scores since we're only half done with our pharm course. I'm taking it June 21st as well - looks like we'll be USMLE Twins.
About USMLERx vs Kaplan: I have both (got the Kaplan for free during test prep week - who woulda thought they actually give out free subscriptions?!?!) and I have completed 850 Rx and 40 Kaplan (just got my script) so my "n" isn't the largest, but I was given some good advice by people on this forum to use kaplan and usmlerx as a basic facts/knowledge/stamina tool and use usmleworld during my board prep as a thinking/concepts tool.
I don't know if that's entirely clear, but I'm using rx/kaplan until my 5 weeks of dedicated time to just make sure I'm used to answering questions, getting through FA, etc. Yeah, kaplan might be nit picky and usmlerx may not have the best written questions... so, I don't know if one is better than the other, but I think doing both is better than just doing one - especially if you can get through a high volume of questions.
As a side note, I've only done 40 kaplan questions, but I really like the few physio questions that I have done.