NIRVANA

I just got this car (the Mustang in my sig) last week and I used to have a 1986 Mustang GT back when I was younger and poor so I didn't have any money to modify it. Now that I have this interesting daily driver I have the urge to mod it. So my question is, since the A4 combined with the sluggish stock 5.0 isn't as fun as it could be, what are your recommendations/experiences with a torque converter in these cars. I know LS1s with TCs make a huge difference, and I'm assuming the same is true here. How big can I go before the car becomes a pain to drive on the street? I need to be able to drive it to work every day so I know I can't go to like a 3800 TC, but I was thinking maybe something a little smaller would be okay.