You'd be the third to recommend the 200R4. In fact, the poster above you said you had a write-up. Is there any advantage to the 200R4 over the 700R4 or 4L60/4L80?
The 2004R is smaller so that way you have to cut a lot less. It's also lighter and doesn't suck as much HP (parasitic power loss). Here are the gear ratios, I think the 2004R has better ratios but it's up to you.
If you build the 2004R with good HD parts (like in my 2004R thread) it should handle 400 horses. Remember, GM used the 2004R in the Grand National (fairly heavy car) and it held up just fine....smoking tires and ALL!!
I personally didn't want the hassle of an electronic transmission (4L60/80). I also used a non lock up converter so that I wouldn't have any wires, solenoids, or switches....just drive and have fun. So it depends on what you're looking for????