If you are using Windows to determine the size of the files, then you don't want go over 4.35 GB.
- Do you want to convert the files to DVD-Video format? 2.Or do you just want to play the collection of files on a DVD with your standalone player?
If 2., then I would just change the extension from .dat to .mpg or .avi and burn them to DVD as data. Then just put the disc in your player and navigate to the file you want to play. A DVD+RW is a good way to test things before actually burning to DVD+R or DVD-R.
If 1. , converting to DVD-Video format won't give you any better quality but the size will increase, (which is why I recommend 2. above.)