sometimes it might depend on the real ntn length of the bow as not all bow lengths aren't listed equally, and there will differences to how they feel at full draw. brace height also plays an important issue.
personally, the shortest longbow for my 29" draw is 62". i don't notice any difference 'tween that and 64", but i do notice a difference going to 66" and a huge difference with a 68" longbow.
so, imo, i don't think you'll perceive much difference 'tween 2" of increased bow length ... 4" or more, yes.