I'm going to share what I have recently learned and gather from other peoples experiences. Back in the day when I was modding a street truck (2004) there weren't many HX40 or WH1E turbos laying around, HX35's weren't easy to find, and S300s were out of reach cost wise. FWIW, please do not bring the S300 into this discussion, as a sled puller I can tell you just how many engineering flaws that turbo has vs the merits of the turbine shaft. I've seen just as many of those blown up as anything else. This is more of a mild build discussion.
I recently acquired a quantity of new holset turbos to play around with. A few local first gen guys have been experimenting with new WH1E (early versions of the HX40) turbos on stock or near stock first gens. We swapped out a WH1C/16 for a WH1E/16 the 16 housing had its exducer machined by a local shop. The WH1E has 2mm additional inducer over the WH1C, the turbine is larger of course.
Test mule 1 was a stock 93 D250 5 speed, it spooled the larger charger pretty much the same as the WH1C. Boost was 1psi lower, possibly due to the larger free flowing turbine, which almost fits in the housing as is. Exhaust sound is slightly different, and acceleration vastly improved 35mph+. He doesn't have a pyro yet so egt numbers are not yet known but we estimate 200-300 lower with the WH1E. Peak boost was 19 psi for the WH1E and 20 for the WH1C, test was done unloaded.
Test mule 2 was a 92 W250 it has very minor mods and 4" exhaust, ill have to get the particulars. The stock H1C/21 lagmaster was swapped out for the same turbo in test 1. Boost peaked at 28psi pulling a trailer heavily loaded. Not really a fair comparison but, again a gain.
FWIW, I currently run a HX35/40W 60x86mm 6 blade/12 on my W350 with a 3200 GSK, Denny T 2 pin, and 4'' exhaust and about 1 turn of fuel. It spools easily, I open the gate at 30 psi, I can run 80 mph with my gooseneck fully loaded with ease if I want. It runs very well. It burns clean if you drive normal. With a 30" muffler all the farmers at the co-op stare as it walks right out of town and down the highway with a fully loaded gooseneck trailer. I see 1250F pre turbo on the pyro if I'm accelerating on a good grade at 65 mph heavily loaded.
What we have learned is the holset 12-16cm exhaust housing wastes alot of energy by allowing exhaust flow to bypass the turbine. We have also decided the VE engines really need more air. In the past pouring fuel in was the solution for more power, it's just $$$ out your tailpipe if you go that route.
My question is reliability of the WH1E and HX40 on a first gen. I know lots of people have broke the shafts on newer heavily modded trucks. Most of which are too hot for an HX40 or WH1E anyway. On a first gen lots of things live that a P7100 truck destroys. I think they may be a better tow charger than anything. I want to build an HX40W/12 with a KTS 60x86 mm billet wheel just to try. The idea is to get the exhaust out of the motor to gain a little more power and mileage, if it can be done reliably is the question.