Not sure how much you're "overrunning" the 3 bar sensor, but if you're only just going beyond what the sensor can handle, it might be better to stick with it and adjust the cells at the edge of the table to accommodate your fueling/timing needs. Remember that FAST will choose the "closest" cells, even when you're running outside of the table. Usually, going with a bigger MAP sensor, the resolution of the rest of the table suffers in order to accomodate the bigger sensor range... as for a 4 BAR map sensor, I do remember someone mentioning such a thing before...try a search!
Justin