SLI, DUAL-GPU Card or Single GPU?

Hi there. I am building a new system for FSX. Here is the hardware:ASUS P6T Deluxe V2 Mobo with X58Chipset ICH10Intel Core i7 920 CPU (d0 Stepping) planned to OC @ 3.5-4.0 GHz rangeProlimatech Megahalems Dual-Fan CPU HSF Air cooling SolutionCorsair XMS tripple Channel 2x3GB (6GB) DDR3@1600MHz, Latency7-7-7-20Nvidia ASUS GTX285 GPU with 1GB VRAM3x300GB Velociraptors with 3 OSs on each. Indipendent of each other i.e. no RAID but running in AHCI mode.OSs: WINXPx86 SP3, WINVISTAx64 SP2, WIN7x64 RCFSX with SP@ Acceleration, FSGLOBAL2008SP1, UTX all releases, GEX, REX, FEX, FTX, ASX, AG, Additional mesh add-ons, MyTrafficX plus other minor patches and updates. On all OSs.2 Displays:Display 1: Philips LCD TV 42 inch @ 1920x1080p used as the main monitor for the outside view and part of the cockpitDisplay 2: EIZO 19inch 1280x1024 for instrument view.My Question is: Am I going to see any benefit by adding a second GTX285 and SLIing? On my current QX9770 system I observe a dramatic drop in FPS when I activate a 2nd windows in my 2nd monitor. I have both monitors coupled to the GTX285. I have around 20fps with one active window 1920x1080 resolution and when I add a 2nd 1280x1024 window, FPS drop to around 5-10 FPS. On my new system this drop will be expected to occur as well but what can I do to minimize it??? SLI? Dual GPU (GTX295)? 2DualGPUs SLIed? Any advice will be greatly appreciated. Especially from NickN and other FSX Gurus.