For normal everyday type of truggy running, either of those combos Mr.BombPop mentioned should work for 4S. I can tell you that I chose the EZRun Max8 G2/4278 2250kv combo for my truggy. I wish I could give firsthand knowledge on the combo, but it's still in the box waiting for rainy catch up on some projects day install.
I don't know what 4000kv motor you were looking at. I'm guessing it was the 3665 4000kv G3 motor. That size motor would struggle, and is only rated for 3S.
If you really want to run 6S LiPo packs, you'd be better off looking at lower kv motors (1700~1500). At least you have a motor mount that orients the motor to the rear of the chassis for many longer can options.