Using a map sensor to add timing has improved throttle response noticably. 2 bar sensor calibrated from 0 to 21.7 psi (full vacuum to 7psi boost) allows the addition of 8 degrees of timing at 14.7psi (atmospheric pressure ie wide open throttle). Will get the car dyno'd to confirm how much can be added at lower vacuum. I'm running 6 degrees advance at lower vacuum at the moment.