the cost and legacy of the e body's vs dime a dozen cheap a body's ( you only need one right?) and the fact a lot of stuff can be transferred to a second higher level build e body later, when you finally get a chance to test the a body against a guard rail or another overly robustly driven fellow track member's car that is going backwards at high speed.

One item in my earlier list I failed to mentioned, tires, other then the driver, nothing else is as important, and unless you are running a stock slant. For performance, nothing is too wide or too sticky, period.