I was always under the impression that the accelerator cartridge was being developed by SOA in partnership with Lockheed, and that AM2 produced Saturn versions of VF3 and Shenmue (then incorporating much more than just the first two chapters - supposedly even the whole story as it existed then) on "stock" hardware, which has been confirmed in the brief details officially given during that interview. I believe that Yu Suzuki has also said exactly the same thing, and that there were two separate completed revisions of VF3. The first was rejected on grounds that an inferior Saturn version would harm sales of Genki's "superior" Dreamcast version (as if this was even close to arcade perfect), while the second was delivered to pressing plants before being ultimately rejected because Sega had already abandoned the Saturn.
The exact performance figures of either VF3 or Shenmue can't be pinned down, despite the fact that anyone interested in the latter has probably already seen the official footage of it. One thing that can be guaranteed is that Shenmue was running at between 12 and 15 frames per second with similar levels of detail to (though still a little higher than) Panzer Dragoon Saga. I've even seen a few people speculate - and it is only pure speculation - that both titles used the same graphics engine, though I prefer to believe that AM2 would create everything from scratch, even if these games date from close enough periods to give this theory some credibility. As for VF3, I've heard everything from 500,000 to 1,000,000 used in relation to its polygon count, though 750,000 seems more realistic. Another idea mentioned enough to be possible is the use of 2D parallax backgrounds in the first revision, which were replaced by basic 3D in the second "final" build. Also, for the winning sequences (where only one character can be seen up close) the models were switched to higher quality versions.
In the past I have written so much about these two games - VF3 in particular - but there's always someone coming forward with just enough knowledge to change the overall picture, so it's difficult for now to find out enough for concrete facts. However, one thing I do know is that nearly everything reported back in 1996-1997 (i.e. the entire "cartridge" issue) was almost entirely untrue. For example, if Core Design were using this upgrade then it would make more sense that it was being developed in either America (as suggested earlier) or Europe, as SOJ wasn't exactly open with sharing its technologies to its Western counterparts - remember the whole Sonic X-Treme episode? What we really need to close this case is for either of the long-rumoured revisions to leak or for some genuine screenshots and video footage. After all, they've already done this for Shenmue. Come on, AM2!...