I have a 1994 formula SR271 that I just put a 496 mag HO in, took it out to test run the other day and spinning a 21 mirage plus with 3/4 of a tank of fuel and two people on board we just touched 60 miles an hour at 5000 RPMs, it came out of the hole very nicely and I don't want to compromise that, but it just felt like it wanted to go more. Does anyone have any advice as to what prop would be best suited for this application

Go to the BBLades web site, download their prop test form and gather data on what you have and call them. They can make a good recommendation, as well a loaner program to try before you buy. Great guys

Your dry weight is 5250 and add gear and fuel your at least 6000 pounds.
If you have a 1:50 drive Bravo 1 then your prop slip is 9.5% which isn't bad at all for the boat. Sure wish mine was the good.

That said, are you reading GPS speed and are you sure your tach is accurate? Your hitting 5K rpms which is the top of the rpm range for your motor. If you have nothing left and not over reving, your probably good as you can get