As far as balancing, the stock GTP38 can install a billet wheel when the wheel itself is balanced and nothing else changes. With the 38r, if you add a billet wheel, you have to get the whole rotating assembly balanced together as a unit. That is where most people have the problems destroying the turbo. If the whole assembly gets balanced, I don't think there is any issue with longevity, however most people still claim that performance is not improved or even worse with the billet wheel anyways.
Moral of the story: if buying a 38r, just accept it for what it is (which is much better than stock). If you want better than that, get a KC38r or go the T4 route.
Ran my original 38R for 14+ years and over 100k mi. Had a problem with the original, factory compressor impeller after that long.
Replaced it with a WW, and was ASSURED by the seller that NO BALANCING is required. I was assured that the wheel is "factory balanced", and the entire rotating assembly does NOT require a re-balance after installation. I then read through multiple posts on a couple forums (including here) where many people said "no balance required" when installing a new WW.
So (against my intuition) I went ahead and installed it. Everything went together fine, and the turbo went back on the truck. Ran it for about 3 months, primarily back and forth to work, and one desert trip.
The WW grenaded while leaving a stoplight (under light load) and destroyed the compressor housing.
I was able to limp it home...
DON'T CHANGE THE STOCK, 38R WHEEL!
There is absolutely NO reason to install an aftermarket wheel in an otherwise good 38R.
Furthermore, the belief that anything with "billet" on it is somehow better/stronger/lighter than something that is cast (and machined) is simply WRONG. If a "billet" compressor wheel was better/stronger than the cast & machined wheel, Garrett would be putting those in from the factory.
Long story long... if it ain't broke, don't fix it. If it is broke, replace it with an original part, not this crap sold as an "upgrade".
I was later informed by a local turbo shop that ALL of those aftermarket "billet" wheels are of Chinese manufacture, regardless of whom you buy it from. And, interestingly, the one I received did not say "Made in USA" anywhere on it, on the box, or on the "instruction sheet" enclosed with it (didn't say China either, but, usually US-made goods say "USA").
I have since replaced the whole turbo with a brand-new 38R. Should be good for another 100k+...