And just what would that new card be? No single graphics card setup needs 700 watts. Are you going to sli?
OP has only one x16 slot on his micro-ATX board so SLI is physically impossible.
Unless he wants a dual-GPU card, a good 450W PSU would be more than enough. From power benchmarks I remember seeing, a modern high-end single-GPU system maxes out at around 350W wall power.