If you do a lot of jumping then I'd stay with the lighter 2 stroke GP1300. The 05 and later GP1300 models have the updated pumps and other features, so I'd look for one in that year range. Doing a lot of jumping is not recommended for heavier 4 stroke skis. You will eventually break something loose. You can still do some occasional wild stuff, but if this is all you do, stay with the 2 stroke ski.
You should get significantly more hours with the 4 stroke. Its hard to put a number on, because so much depends on how the ski is maintained, but in my experience most 2 stroke skis will need some type of engine overhaul around the 300 hour mark. You will find exceptions. That said the Seadoo Rxt is a nice ski, but will need some work on the supercharger every couple of hundred hours. The Seadoo will also be a little harder to maintain overall. If you are riding in brackish or salt water the Seadoo closed loop cooling system may provide an advantage.
Both the GP1300 and the RXT are pretty hungry for fuel, so you will be spending some time at the pump.
If you plan to ride 2 up most of the time you will probably be much more comfortable on the Seadoo. The GP1300 is a 2 rider ski, but that really means 1 person rides comfortably. The Seadoo RXT is 3 person seating, which really means that 2 can ride comfortably. I don't see any advantage at all to an RXP, so I'd only look at RXTs.
2008 Yamaha FX HO Cruiser
2010 Hurricane Sundeck 2100