The GP1300 is a fast ski to start with (66-67 mph stock). If you have never ridden a ski before, 60 mph on the water will feel like 120 mph on a motorcycle. Until you have been riding for a while you will not be able to maintain 65 mph on the water unless it is very calm (I'm talking glass smooth). In the ocean, or on rough lakes, you will seldom be able to go faster and stay on the ski, so speed becomes much less important. Professional riders are lucky to maintain 60 mph in rough water conditions.
But, if after you have mastered a stock GP1300 and still need to go faster, there are modifications that will put the ski over 75 mph (but be prepared to spend $$$.........just a few mph cost big). Riva Motorsports, and R&D Performance, are just 2 companies that offer modification kits for the GP1300.
The fastest skis right now are the 4 strokes. The Yamaha FZs will do 68 mph stock, and guys are pushing them up to 90 mph with lots of very expensive modifications.
I don't know of any specific problems with a GP1300r, but it is a 2 stroke, and it is basically a 1 rider ski. Not a ski to buy for a family to tow the kids with. It is also known to be a pretty big fuel hog, but so are most of the skis that will reach 67 mph stock.