Looking at the PP FAQs, you can make additional (unscheduled) payments to pay off quicker, but it's unclear whether the first and second scheduled payments are affected by doing this. If they are adjusted, it means you can make the purchase, make an unscheduled payment, and the subsequent payments would be reduced. But I would check with PayPal themselves.
Erm... Thats exactly what I was going for xD I get about 50fps steady, 80 to 90fps when nothing is much is happening on epic settings, so more frames would be good. My GPU is almost a year old though so I'll keep that along with my HDD's and SSD, hopefully putting them in a more up to date rig. the CPU etc was spec'd for ARMA 3 to put an age on it, so everything else, so could use an update.