Well, a low end card like an HD5450 or even onboard video can handle everything but the gaming... for $200 a GTX 460 is what you should be looking at for gaming at that resolution. Whether that is worth the extra $150 or so in order to do some "very infrequent gaming" you have to decide for yourself I guess.
BTW that PSU is overkill. A unit like that is intended for high end multiple video card setups. A 500w Corsair or Antec would be more than enough or 400w if you don't bother with the GTX 460. Also why on earth would you need 16gb of ram? more than 4 is mostly useless to a normal person and your processor/motherboard is LGA 1366 which means it uses triple channel ram so you will want 6gb(3x2gb) of ram, not 8gb. Or get 12gb I guess if you really insist on pointless overkill.