With PMDG incorporating the confiqurator to use lower texture quality. I believe it would perform as well if not better than iFly on lower end systems. The Wilco V2 737 can tax a low end system also. If ones concerned about performance, should look at the Overland/Simmersky models. No FMC and not as detailed but that's what make them easy on performance. Specially with those specs!
CPU: I7 2600K @ 4.7 ghz, GPU and CPU water cooled
GPU: EVGA GTX 680 OC
MEM: Gskill Rippjaw 1600 12800
MB: Asus P8P67 Pro V3.1