First, please do not confuse the compatibility (playability) of the DVD players with the quality of DVD-R discs. You can use the best quality DVD discs burned by the most expensive DVD burners and still not playable in your player if it doesn't support DVD-R(W) and DVD+R(W). Check out the DVD players list from dvdrhelp.com to make sure your player is compatible with at least one of the disc formats:
Also if you are planning to burn the mpeg files on the DVD discs as you mentioned, you have to make sure that your player will be able to recognize these files on the DVDR/W media.
Both DVD burners are not very good at burnong cheap 4X DVD-R discs at the rated speed, although the NEC model does a better job with the recent 1.06 firmware update. If your DVD player is compatible with the DVD+R discs, then I'd recommend buying the brand name 4X DVD+R discs (normally $1.20 to $1.50 per disc when they are on sale), and it takes around 15 minutes to burn a full disc of 4.3 GB.
As for the 8X burners, they'll be overpriced in the beginning and the 8X media probably won't show up on the market until the year end. The Sony DRU-510A first appeared on the market in May, which is able to burn the DVD+RW discs at 4X, and so far I still haven't seen any store selling those 4X DVD+RW discs. If you don't mind paying a premium for being an early adopter without much practical benefit, you can preorder an 8X DVD burner from Plextor, while other manufacturers won't introduce their 8X models until November.