Jetting is a fussy business. You can dump all the fuel you want into the cylinder, but if there isn't the air to mix with, you'll just being wasting your time and money. Flammables all have a high limit flash point. Exceed that limit and you wont get any ignition. So by increasing fuel intake to what is calculated to be burned with 500 cc's of fresh air into 425 cc's of space will not give you the response your looking for. It could however cause premature wear on things like your crank, wrist pin, rings, etc.
I'll use the horse analogy; you wouldn't expect a Clydesdale to out run a thoroughbred, but if you want to pull a tractor from the mud it's a good choice. But race horses don't spend anywhere near the time racing that a Clydesdale does pulling a plow. The harder you ride the more you'll be repairing.
If you want more power, first you have to know which kind. The 425 can be reworked into a 500. Are you after speed, torque, throttle response? Have you considered dropping a tooth on the output sprocket or changing the drive sprockets? The 425 and 500 use the same head and valves. So Polaris did their homework on what to change and where. Engines need to breathe. More air, more fuel= more horsepower. Try moving your jet needle and see what you get. Your main jet shouldn't be increased any greater than the largest Polaris lists for altitude changes in their service manual simply because the fuel just won't burn properly anyways unless you can get more air flow.
