Yes, best to compare the Naish Freewide to the Futura or the Isonic to the SP. The SP is a dedicated race board, not freeride board.
Will the Futura 144 replace your 165 Go? For the most part yes, unless you are sailing in really light winds where the added float will make a difference in schlogging. In planing conditions you would probably end up shelving the Go for the better performing Futura as those two boards are very close in sail range.