I play at FSX in 1680*1050 and even my HD 4850 suffices, FSX has need a good CPU (core I7 or Phenom II X6). The HD 5850 will be suffices
What CPU do you Have ?
... 1680*1050? I actually interesting to use TREE monitors...
Anyway here my CPU: Intel Core 2 Duo E8500 Tray 6144Kb, LGA775, 64bit