Thanks for your replies, gentlemen. I feel a little better about popping a heavier spring in my black cylinder now.
The previous owner gave me a couple of "dead" motors that he had lying around - apparently they need to be rewound. Is there anywhere online that can fix these up and get them functional again? I'm pretty happy with the FCC 2.0 motor I have in there right now, but I've heard horror stories about motors dying and I've love to had a backup or two just in case.
I must say I'm thrilled with the performance of my PTW. Granted it was pretty heavily upgraded by the previous owner so it's far from stock, but I'm still impressed with the accuracy/range I'm getting out of it. By far the best performing airsoft replica I've ever used. Glad to be part of the club.