Well, many will say (and most benchmarks agree) that [CD] drives are nowhere near fast enough to make use of 8MB of cache. DVD-R/RW drives have quite a bit more throughput than the standard optical drives, so they may actually be able to make use of a large cache like 8MB.
Hard drives, however, have done well with the extra cache. But I don't think the performance difference is
very noticable. It is noticable, though. Considering the 8MB cache drives are often just a few bucks more, they're a better buy. But sometimes you can find a 2MB cache HD for quite a few bucks cheaper than it's 8MB counterpart, in which I would say go for the much cheaper drive.
Did that help? If not, check the benchmarks & reviews on the particular drives you are considering.
http://www.google.com/search?hl=en&l...benchmarks+2MB