I have read elsewhere that the GFS model overstates the pressure levels (in the bad direction) by as much as 50 mb, so that 891 number might not be what it seems.
GFS is better for track than intensity, but Irma is already at 944 mb and is entering some very warm waters. Best case for the US (and nightmare case for Hispanola) is for Irma to get close enough to that island for some disruption of the circulation. Cuba won’t be much help, the midsection of the island is pretty flat.