There is some overhead, if you have menus, and mabey some for chapters and all.
The 4.7GB disks via my costly authoring tool, sets the disk file size for the creation of a consumer compatable Video DVD at 4393.08mb. I think I have wedged more on it than that, and stopping at this 4393 does leave some unwritten space as seen on the back of the disk.
Generally speaking , it sounds like the problem your having is trying to stuff all of 4.7G on the thing. If it will take 4670 (which I doubt) , then you should shoot for way less anyway, .1%-1% changes in overall bitrate, is not going to change the picture much.
Where they get this 4393mb number from I dont know, but that is still less than a whole percent, on 15-1 20-1 and 30-1 compression ratios 1% would not be a noticable increase in data loss.
When it comes to a disk breaking down (delamination) , which happens on the edges, and sombody putting a fingerprint on it, using this last bit by whatever method is not going to improve longevity and compatability.
The burner software should be identifying the disk itself after the disk is inserted, most of the disks have some sort of code on them, that IDs the disk , and the speed and all.
"Nero" for one did allow for overburning of cds and DVDs, the quantity was 4500-4600 or something. only if your already stuck with a ISO of that size , would it be worth it to do that, anything else or anything that you intend to pass on to normal consumer players , you should not do this.
The disk will write fine and playback fine, but if a device has an "issue" with this over bit at the end, only playing that actual end of the disk would show the problem, Make Sure you check all the way TO the end. Ending cold on a dvd playing on an OS , could cause the player software to crash. (luckily the OSes dont crash with the programs as much anymore)
Notice the comment, same as mine .
Overburning is a great way to brick a disc. . .