to original poster,
I recommend taking the October PGRE test. I had registered for October, but changed to November - then it stunk that I hadn't gotten my score by the time I sent my applications that were due Dec. 15. Plus, if it goes badly you can do the November test too.
Also I took the General GRE mid December (it only takes 2 weeks for the scores to get done for the general) and the Dec. 15 deadline schools will usually accept GRE scores a couple weeks past the deadline. But I didn't like taking it along with my final exams - I was tired, stressed, and I didn't have time to do any practice exams because I was studying for finals (and so I scored badly as a result) ... so I recommend taking it by August before your fall term begins. Then you're done and you can focus on subject GRE preparation.