If you get a 450+ string that's the same diameter/weight as the 8125, shouldn't be any noticeable difference in performance. 8125 is more durable. If it were me, I'd stick to 8125.
The difference is 8125 is 92% Dyneema (think the other 8% is Vectran, but I'm not sure). 450+ is 70% Dyneema and 30% Vectran. 450+ is a much larger diameter strand--if you try the 450+, don't get the same number of strands in the string as you have with 8125. 450+ is approx. 155# test per strand, 8125 is approx. 120# test per strand.
Dynaflight '97 is my first choice in bowstring material, with 8125 running a close second.
Chad