DO a 4K. You won't regret it. It will be an absolute animal,and if you have lockup, whats the big deal? Don't go cheap though. Go with a precision industries or yank converter. Expensive yes, but they each give you a free re-stall, and they won't come apart and damage your trans. Even one with a documented fresh re-stall would be good. The PI vigilantes run a bit loose, as do the yank PT's. The yank SS's are about spot on.
For reference my vig 4000 would actually flash to 4400. MAN would that thing get you moving.
HOWEVER
4K might be a bit much on a turbo car. SO, you might be happier in the 3K range. IDK, that's just LS1 fbody knowledge dripping out.