Someone has a nice comparison video up on YouTube.https://www.youtube.com/watch?v=NDgzZ2rEQTM
Other than the ocean in the opening stage of Outrun 2 SP which visually looks much better on the Xbox version, it's tough to tell the two apart.
I've owned all console versions Of Outrun Coast to Coast, including the needs to be reviewed PSP version. They are all very similar. One thing I noticed is that the Xbox version actually would have an infrequent but weird choppiness from time to time. I eventually sold the Xbox version years ago simply due to it being so pricey.
With all that said...I actually own a four arcade machine setup of Outrun 2. It's at a charity arcade I help with south of Indianapolis. If anyone is interested in going there, let me know and I will get you some complimentary passes.