It came to a surprise to me too. jPCT beated xith3D in that Quake3-level earlier even with the default pipeline, but some years have passed since then and i thought that the situation might have changed. Obviously not. The performance of the different engines is very interesting IMHO. Both machines have identical CPU power as long as you don't use more than 2 cores, which none of the engines does. In fact, i think jPCT is the only one that can offload at least some load to another thread/cpu. The high polygon car should be GPU limited. In jPCT and xith3D, it seems to be. In JME, it seems to be solely CPU limited, because otherwise, the much more powerful ATI should beat the crap out of the GeForce...but it doesn't. It's actually slower...
The Quake-level on xith3D suffers from whatever...maybe too many state changes or something. jPCT largely benefits from its past here IMHO. Because it's geometry throughput was always limited, i tweaked every other part to the death. And the compiled pipeline is still using large parts of the default pipeline, like the state sorting, the state management and such. This seems to pay off now...