I literally melted my MBP with the same specs as yours doing UE dev. This was partially due to Apple using substandard solder, but maybe their future models won’t suffer with this type of issue. When doing UE dev with the editor running, I found the was thermal throttling at basically the max operating temperature of the processor.
Basically I’m looking for something that is proven it can handle the heat 
Also, I don’t think Apple is going to move away from something like the 650m because of its lower operating TDP and I’m a real big fan of the 9xx series.