Holy man.
You've got a ton of problems here...
1) You're using poly in a full bed at 60lbs. Awful idea.
2) You've left it in FOR SEVEN MONTHS.
3) Poly isn't meant to last more then 12 hours tops. The only time I've seen people use it for a longer time is with Natural Gut in either mains or crosses to really soften it up after the string dies.
Honestly, I wouldn't be surprised it you're arm just decides to quit on you!
Do you really need poly? I know it seems like a trivial question, but since you can't string basically weekly, what do you gain from using poly? You say control, but stringing that high you could probably use just Synthetic gut and gain the exact same amount of control. From the sounds of it, you're not a string breaker if poly lasted you seven months.
I'm not trying to pick on you here by any means, I'm just trying to make sure you can keep playing tennis for a long time!
Little story here. I had a friend who was a junior back in the U16's. The guy played a Pure Drive Roddick +, Full bed of Lux BB at 64lbs. He was really confident that he was playing well. Sure he was winning and hitting really big shots. (He broke his Lux Weekly.) Guess who's not playing tennis anymore though? Once he hit 16-17, he can't even hold a tennis racket anymore. He's been going through Tennis Elbow treatment for the past 8 months, just so he can do everyday life things again. He can barely write in school, which has become a huge issue.
Needless to say he probably won't ever play tennis again, which is a shame because he's a great guy and he was a good player too.
Just be careful with you're choices! It's you're body, but just be aware what you are doing to it!
-Fuji