I had the 3800 in my slash 4x4, and although it didnt run hot, it was a little toasty, even at stock gearing. It wasn't all that fast either, even compared to the stock motor. much more torquey though.

look at ebay! seriously. people are parting out platinum and ultimate slashes. this is good, because you then get to pick your body, tires, and electronics separately. they were about 250 for a brand new chassis i think.