Honestly, it depends on your comfort level with how much boost you want to run. Here's what I mean,
With the T64E (which already has a 66mm inducer comp wheel) you will need to run the boost up to 25-26psi in order to achieve mid 10's with good 60fts. Now, depending on how loose your converter really is, you might have to have it loosened up if you go with a non bb PT70 GT-Q, which with combos such as yours needs a converter that can flash stall to 4000. If you go DBB 70 GT-Q, your converter should be fine and you probably won't have to run more than 23-24psi to reach your mid 10 goal. IMHO, I wouldn't upgrade from the turbo you have to a 67, there's just not that much more to gain considering the cost. 85 more hp capability when the boost is maxed out for $1,500 is not a worthy upgrade to me, unless you could sell your T64E for say $800.00, then it might be worth it. But, upgrading to a 70, even if you went with a PT7076 P-trim equipped turbo, then you would gain a significant amount. The T64E is rated to support 700 fwhp when maxed out. The P-trim 7076 is rated closer to 845 fwhp.
DBB, no need to change converter, non BB, you will have to change the converter if you go with a turbo that has a GT-Q turbine wheel. There are a lot of folks who have run mid to high 10's with the turbo you already have.
Just my O2's worth.
Patrick
