no a 70mm is fine. meter size is GROSSLY overrated. check out livernois motorsports mustang. it runs 7's and i think it has a 105mm (apx 1100 hp)
no, the gt40 is great, ported it will support 400 hp (do you have a tubular, cobra, or explorer?)
i would go 4k on stall, absolute min of 3000...