No, no, no - don't even think about FSX as being a useful tool in these circumstances!
I've never used FSX but I have tried EFATO with a Cessna 172 on FS2004. As long as you actually stop the engine it gives a fairly realistic idea of reality. It showed me that, depending on conditions, anything more than a 90 degree turn is not on below about 800'. The actual limit depends on wind strength and the size of the airfield you have just left. E.g is a down wind landing a viable option?