Even then there are different sized compressor blades you can run, each will have a different affect on the way the truck performs. There are several rebuilders out there that can mod your turbo. Elite, Spartan, Industrial Injection and many others...just think about what you want out of your truck and then make some calls.
Your OEM variable vein turbo can be modded to perform to what your intended use may be, if you choose to run a fixed turbo there are those out there to fit your truck, IF you want the best of both worlds a set of twins could do the work just fine.
To say there are only two kinds of turbos isn't an accurate statement. The VGT-SS and VGT-HO are produced by one company. Turbonetics, Industrial Injection, Spartan Diesel ALL have turbos of simular design and technology.
I stand by my orginial post...DECIDE what you want the truck to do (tow, sled, drag racing, etc.), make some calls and talk to the builder about what you want and how they can help you decide on what to buy. When you do you will see a new turbo isn't an easy choice to make.