I think this is a major factor in the snow blockage you are experiencing. Wet snow doesn't help at all, but if the blower is running too slow you can pretty much count on trouble like you are experiencing.
I ran my blower at 2000 RMP or so for the first few times because I was still within the 50hr breakin period, and whenI was finally OK to run at full speed the difference was remarkable. It was all in dry snow, mind you, but the difference was clear. All the other suggestions folks have made here are excellend and will help, but if you aren't running at full speed I think you will find yourself in an uphill battle.
Some 3PH implements can be run at varying PTO speeds, and some really require the full 540 RPM. Chippers, mowers, and snow blowers are three than come to mind (probably becasue I have them). Others like winches and backhoes can run at any speed that suits your needs.
As others have mentioned, I wouldn't worry at all about running at full speed. The macine is designed to do just that day in and day out for thousands of hours. Headphones or ear plugs are a must regardless of the speed, in my opinion.
Good luck and I hope you find satisfaction in your snow blower. I'm quite happy with mine.
P.S. You do have the advantage fo multiple PTO gears and could take advantage of it. Assuming your 540 PTO engine speed is about 2600RPM when using the 540 gear setting, then about 1800 RPM will give you 540 PTO RPM in the 760 gear setting. I would recommend AGAINST over-reving the blower using the 760 gear so don't crank the engine up to 2000 RPM inthe 760 setting.
My only complaint is the amount of shear pins I been through. I've used it three times very successfully and broke three pins.