Barrel length has nothing to do with accuracy at all strictly speaking, in fact shorter barrels are less affected by harmonics and are actually more accurate in many cases.
There may be some difference in velocity between the 26 and a 20, but can promise, it aint much (I would be shocked if it were 75 fps), AGAIN faster DOES NOT mean more accurate. The optimal load will take experimentation on your part, but the bottom line is that these are factory barrels. some are really good and many are not. At least in an LTR you have a rifle that is extrememly suited for upgrades, including a match barrel - in any length you want. This would turn that rifle into a potential competition winner.