I replaced my journal bearing GT4067 (.82 T4) with one of the new (air cooled) ball bearing PT6262s (.68 T4). Since I road race mostly I decided to get a slightly smaller turbine housing to try to get as much response out of it as I could. My old turbo used to get full spool around 5200 rpm and the new one gets full boost around 4500 rpm. To be honest I actually expected it to be a little better. I may actually try a .82 AR turbine housing, although it does go against conventional logic, I almost wonder if the .68 is choking it a little bit.
For reference the old 67mm GT40 was definitely a bigger turbo and so I expected I may see a slight loss in power. However the PTE 6262 is one of the new billet series turbos and although it is only 62mm it flows like a much larger compressor and although it is almost the same size as the standard 35r it can flow quite a bit more. In fact there was an Evo with a .8X T3 based 6262 that made almost 800whp and went into the 8s on it!
It actually turns out that the new PT6262 seems to make more power than the old turbo when I run around on my street boost (i.e. 17psi, which is wastegate pressure). At 24psi it likely makes less peak power than the old GT40 did however there is more usable power under the curve and I found that it actually bested the old turbo in 1/4 mph even on 24 psi. At the track I had to let out on my only 17psi pass because the car was got a little twitchy at the top end of the track. But I'm pretty sure it would have trapped somewhere around 126-127. On 24psi it did a new best mph for me of 136.
Overall I have been very happy with it and would definitely recommend it to anyone looking. The journal bearing versions are VERY VERY cost effective!Here are the overlays. The lower pass was 501whp/375wtq and was made at 17psi. The upper pass was 564whp/441wtq. It was a 24psi spike, however because the dyno load was a little lower than on the street the boost dropped to around 22 by the end of the pass. You can see it in the torque curve a bit. I didn't have my laptop there to make any adjustments but it probably would have made a little more power on the top (likely another 10-20whp and maybe a *touch* more torque). The car is on e85, mustang dyno.:
As an aside I only made 2 passes because I was really there to tune my buddies crazy a** GN for him. It made 1620 at the tires on ~24psi and e98.
Then an intake valve dropped, but not sure why. It doesn't look like it was a tuning issue (I was tuning it, and there wasn't a hint of detonation and all air fuels looked great), and it doesn't really make sense that the valve would have floated either. But it definitely chewed up a cylinder head and piston. 
I feel bad for my buddy its like we always take 2 steps forward and one step back. Oh well, I guess that is just the name of the game when you create a car that really pushes the envelope.Here is a nice pic of his setup:
A fun "for reference" shot. It shows my 4" inlet compressor housing on my turbo next to his.
sweet pics and nice numbers 
