How much does EMT conduit installed vertically on a poured concrete interior basement wall have to extend beyond the top of the concrete?
4 inches was a good call.  It gives you room to get above the schmutz from pouring concrete and get an EMT coupler on the pipe, and gives you some spare distance in case the pipe's end gets damaged and needs to be cut back a bit.  

The ruling factor is whether you can get an EMT coupler on it. For that I'd recommend at least 2".