I know, I know. But for sheer responsiveness, you can't beat it as long as you can deal with the limits of the sound palette.
Mark Smart, who I think is on this list, came up with a design for a GR300 CV interface (
http://www.marksmart.net/gearhack/gr300/analogmods/395report/Report.html) which intrigues me greatly, If I'm not mistaken, CV to midi conversion is very fast and accurate. If one had the dollars to throw at the problem, it seems like a CV interface based on the Roland pitch detector circuit of the GR300, which in turn fed a 6 channel CV to midi convertor would really be the best tracking midi guitar controller of all time!