I agree, the rigging will be sloppy loose if 1/4" wire is tensioned to 267 lbs (3.8% of breaking actually).
Also, if you are planning on upsizing the wire, remember to upsize everything else from chainplates to turnbuckles to mast tangs to match otherwise it is a waste - and regardless the load on the boat is greater.
Wire seldom has a load problem - mostly it is a corrosion issue. Larger wire will corrode as fast as smaller wire.
Living aboard in Victoria Harbour