I don't think any PC is good enough to use FSX with every setting at max with no stutters.
However, the system you propose would be pretty good with most settings near to max subject to making a tweaks or two here and there with the fsx.cfg and maybe the operating system.
Most of all, to get the best out of FSX, you will need to overclock that i5 to around 4 GHz, so better get a good aftermarket cooler to go with it.
Q9550 @ 3.78 GHz with Gainward GTX570 1.25 Gig DRAM
4 Gig DDR2 RAM - Windows 7 64 Bit
Resolution 1680 X 1050 X32