I have a BDR-208M (aka BDR-2208
), and I experienced similar issues. This was my first Blu-ray burner/reader, and I installed it in a Vantec NexStar DX case.
Although the unit is rated between 4x and 8x for reads on BD-R (depending upon the optical media), I found the performance to be inconsistent. When I would rip discs, some would give me great speed, and others would just throttle to the minimum (i.e. 2x).
Obviously, time is the great cost for the ripping and encode process, so I started exploring my options early on. I ended up buying an LG WH165NS40 to test as an alternative, and I never looked back. The performance was so far superior to the Pioneer that I left it behind. Recently, I had issues reading an older disc, and I dug the Pioneer out of mothballs. Using another Vantec external case, I found it still performed similarly to the early testing a couple of years prior (using a more current OS, etc.).
When an optical disc standard first gains widespread adoption, there are many variants of optical disc media on the market. Eventually, the market settles on a particular "standard" as to what media is most commonplace (especially the film distributors), but drive manufacturers are challenged to try and account for all of them. As an early player in this space, I believe that Pioneer made units particularly sensitive to the type of media being read.
In short, I'd suggest it's the drive. Based on the anecdotal feedback I've seen (including the posts in this thread), I believe the Pioneer units run on the conservative side for accuracy over speed. I believe there is a case for this (especially when you may have trouble reading an older disc), so it has it's uses.
I recently built a dedicated ripping and encoding rig, and I've taken both the LG and Pioneer drives and installed them into the tower case. My primary driver will be the LG, but the Pioneer is on standby any time I want to run it. It's also fun to run simultaneous rips (saves time), but the LG wins every time.