For one...what version of FS are you thinking...FSX will never max out on current hardware available...FS2004 is pretty doable for around $1000.
Two...80-100 Frames...no point...the human eye cant even detect that and you will never get even FS2004 to do that maxed out. 30-35 FPS in FS2004 is incredibly smooth and perfectly doable

I have never had any Simflyers scenery or payware aircraft so don't know how framerate friendly they may be. But my new system I finished early last month runs FS2004 completely maxed with some pretty detailed freeware scenery and a Meljet 777 which used to bring older systems to a crawl when in outside view...Its locked in at 30 FPS which is perfectly smooth and never see them drop.
Specs:
Intel Core 2 Duo 3.0 GHz E6850 CPU with a 1333 MHz FSB.
2 Gigs PC8500 (1066 MHz) DDR2 Dual Chanel RAM
512 MB PCI-E GeForce 8500GT DDR2 Graphics Card With DirectX 10.
Gigabyte S-Series P35-DS3R Motherboard.
160 GB SATA 3.0GB Hard Drive.
430W Thermaltake PSU.
DVD/CD Burner.
Windows Vista Home Basic 64-Bit.
Cost about $1000 USD to build (Just the tower).....Mind you I already had the power supply and DVD/CD burner. Couldn't be happier with it. 8-)