Clif, You may know this, but one neat feature of the 8000 is the Groove Function. You can easily make changes to any onboard style. For example you can take a 4/4 rock beat and make it a shuffle, change the beat locations and make other groove adjustments. Then you can save it in the Groove Style Bank. Once you play around with it, you'll be able to make some outstanding "new" styles.
On the PSR740, and I think the 730, this is done automatically simply by pressing the Groove button. The 8000 (and 9000) makes it harder to do, but increases the options available also.
And it does let you save them. Oh, incidentally, once you create them, Groove Styles and Custom Styles are the same. You can move them from one bank to the other on the 8000. I found that they usually work better when saved as Custom Styles. Had a few glitches on some of them when played from the Groove Bank. I remember they used to "forget" volume changes and tempo changes.