Dave, it sounds like you're approaching the point of diminishing returns in regards to the streetability of your ride. Eventually the HP increase (and supporting modifications) are outweighed by the decrease in practicality.
Having said all that, I've got a 4-cylinder converter in my Z, which has a stall speed about 400rpm higher than the 6-cylinder one, and it's a pretty good thing. I'm not sure if fitting a CA or SR converter would be feasible or achieve the same outcome behind an RB, but it might be worth talking to MV's about your options.
But do have a care about the well being of your gearbox - heat kills and stalling up makes lots of heat...