Let me put things down in an objective way and then you decide :
Improvements of the 2166D over the 5163D/B? :
- do you really need lightscribe?
b. faster CD-R burning speed - 48X (40x with the 5163)
- this basically translates into a CD-R burning a few seconds to a minute faster than with the 5163 and is really negligible.
c. faster CD-RW burning speed - 32X (24X with the 5163)
- this gives a slight improvement in the burning time for CD-RW discs but again probably isn't that big a difference.
- how often are you going to burn CD-RW discs? Can you stand waiting a little bit longer?
d. DVD-DL support
- DVD-DL discs 1. expensive right now, 2. have poor compatibility with DVD players, worse than DVD+DL in fact. 3. not that easy to get hold of
- unless you absolutely need DVD-DL support, this is really not an issue
e. faster DVD+DL burning speed - 8x
- 1. as with DVD-DL discs, expensive. 8x DVD+DL media is very difficult to find
Disadvantages of the 2166D as compared to the 5163D/B? :
a. only has USB 2.0 interface (5163 has both USB 2.0 and firewire)
- do you need firewire?
b. expensive because it is the latest stuff on the market
DL discs right now are really too expensive when you compare their price to that of DVD+R/DVD-R discs. They simply cost to much to be worth using for backing up data. That leaves burning movies on them. Unless you absolutely need to have DL movies as a 100% identical copy of the original, many people prefer to use movie compression software (e.g. DVD Shrink) which will compress a DVD DL movie to fit a normal single layer DVD+R or DVD-R disc. Quality is slightly compromised because of the compression but is usually acceptible.
Weigh up the issues and see what is really important to you and what is not. Compare that with what you need to do with the drive most of the time. If you find that you don't need the extra features of the 2166, then maybe the 5163 will work fine and save you a bundle as well.