Years ago I swore to never again use a drive overlay and now they may be coming back to haunt me.
I used to run into all kinds of problems fixing my friends systems that had these damm things.
Keep in mind that if you use a drive overlay you are using a non-standard disk translation to access your hard drive. Several hard drive utilities will not work, or your going to need work-arounds to use them. Things like ghost, drive image, partition magic, etc.
There is only one sure fire way of removing an overlay, that is backing up everything to a smaller drive (that doesn't need an overlay) and then fdisk'ing and formating the drive. Even then, sometimes you have to zap or wipe the drive to remove the overlay from the fat table.
Following the manufactures instructions in removing the overlay from an existing drive full of data is not 100%, you still risk loosing everything.
Thats my opinion, take it or leave it.
This is what I would do, and you may want to try it in your experiment.
Manually set the partition to end before the BIOS limitation.
For your 8gig drive your testing, set the partition to end before the 1024'th cylinder boundry.
You stated 8.4GB as the limit, so your using something thats figuring a meg as 1000 instead of 1024. In that case, set the partition to end at 8001 MB (1019'th cylinder boundry. It's actually less than 8gigs using the actual count of 1MB=1024kb)
In other words, do not let fdisk set the partition to 100% of the drive because it can't properly see the whole thing.
Sacrifice a few extra megs and manually set the partition to end before that. Later, when you update the BIOS you can use PM to expand the partition and take less of a chance with partition errors.
As for the promise card, have no idea and I'm just guessing it won't work. Even if the card supports a drive that big I don't see what good it will do you if the BIOS can't get to it.
Best of luck
Dave