I think the new chassis is a must have for medium-large outdoor tracks with 1/8 scale jumps. If I understand it correctly, the center diff will be slightly further away from the rear diff which translates into a substantial change in weight front to rear weight distribution. As mentioned before, you can't replicate the 3mm built into the chasis by just changing the wheel base.

I have decided to get the new chassis now (direct from AE) and I'm going to wait for the rest of the parts to be available at hobby stores before I buy them.