After about 16-18", the length of the barrel will not "improve" accuracy, its all about the quality of the barrel at that point. Tac-ops (and others) loves the 20" barrels, they seem to get the best accuracy using that length. In fact, the remtington LTR with its 20" barrel has been more accurate then the standard 700P on average. What is most important is the quality of the work on the barrel. If your smith is good, you may see better accuracy if he does an excellent crowning job. If you have a good smith, I would have no reservations having the barrel shortened.
Personally, I prefer 24", the rifles just seem to balance better for me, and are easier to handle (and a bit lighter) and still get me the good velocities. My bravo-51 has a 22" barrel, its nice also.
MEL