Stick with the tubby! I tried the 3racing chassis, hated it on asphault. Its too stiff and made my car lose all its grip I had come accustomed to. I went back to the tub, and made use of the FT/Rear graphite gear box braces and nice blue aluminum ballstud carrier.
The graphite braces simply slip on the side of the gear box, then the blue aluminum carrier goes on top and gets screwed down, and holds the graphite brace in position. You will then need to add washers/spacers (3mm) under the brace where it screws into the chassis, you'll see what I mean if you do this. It may not be any better then stock, but it sure makes it look good!