The 320 and 540 had a few nice things going for them: You could option them with the same 1600SW monitor that the higher-end O2 workstations used without having to use the fiddly multilink. SGI paid Microsoft for a HAL license and did a better job with multiprocessor than what you got from installing the vanilla version.
They had decent bandwidth internally allowing them to playback uncompressed realtime standard definition video which normal PCs running Windows couldn’t do at the time.
The moment your product runs Windows, it'll compete with thousands of others. Being able to do one single thing better than the others won't help you much unless that one single thing can drive all your sales.
Even for video rendering, if your box is twice as fast, it'll be outcompeted by machines that cost half as much or less. At times my desktop PC was not fast enough, it was simpler to get another PC and run time-consuming things on it while I did other things on the other.
