It's not a Slash, but a very similar 2WD. In this case, it's my now discontinued Losi 22S SCT on 3S in a field. This had, at the time, a HobbyWing 3150KV motor, and 60A ESC, which didn't last long.
And, this is my Slash on 2S with an Aarma BLX100 ESC and 3700KV motor.
In a straight drag race, they were about even, which is when I learned that KV should be paid close attention to. In this case, on 3S the Slash ran way too hot, and had issues, whereas, on 2S, the Losi was slower than my, at the time, brushed HPI Blitz. The biggest lesson I learned was that, pairing the right battery to the right motor and ESC and gearing it for the vehicle is very important. Before you decide on a 3150KV or 3700KV, first decide which you are going to run more, 2S or 3S, and go from there.