The T38 record is 209' 8" - 38g shooting head.Well, if you look at the BFCC senior distance records the 'can' ain't that big . . .
5wt - 138' 3" - 9.07g
7wt - 146' 6" - 11.99g
9wt - 148 3" - 15.55g
. . . 10ft over 4 line sizes in competition conditions.
Mr Normal Angler isn't going to guarantee himself extra distance by using a fly line that's 4 sizes larger and which weighs the same as a 10p piece more. We choose our line sizes to suit where, how and the the conditions within which we're fishing. Distance is only one variable and not reliant on weight.
This is obviously an extreme example but I'd argue that a shooting head line will probably give an average caster more distance.