They tested dual-wielding on mythbusters, it's absolutely of no advantage. You can't shoot faster or better since the gating factor is not the gun (you can shoot semi-automatic pistols extremely rapidly) it's the ability to focus and aim more than anything, both of which are hampered by dual-wielding not improved.
P.S. In terms of raw cool-factor, it's hard to beat this: https://www.youtube.com/watch?v=3tEYcUSQDyw
I won't spoil it by describing it.