[1] http://hardkernel.com/main/products/prdt_info.php?g_code=G14...
I was investigating corruption and performance problems with our root filesystem on an SD card. The cards would be great a obvious benchmark style tasks, but when I recorded the block access pattern from our driver and replayed that on a Linux desktop with O_DIRECT, we'd not only get under 200KiB/s average access speed (which matched what we were seeing on the embedded system), but we would also get corrupted sectors (ie. we write it just fine, but we just get an error back from the card when we go to read the sector) in less than a day of sustained writes (once again at only 200KiB/s). And this was with high quality SanDisk cards that were then verified by them to be real cards (for a while we thought that clones had made their way into our supply chain). Using a weird form factor eMMC chip in an SD card got rid of these issues. There's also "industrial" SD cards that are around the same price that I suspect are basically the same thing.
That being said we tried many different SD cards from quality vendors and found pretty heavy bugs and performance related issues among all of the non "industrial" versions.
So, yes, the problems don't have to be intrinsic to the form factor, but empirically you're more likely than not to have issues with them.
I'm only getting 100-150MB/sec on rotating media today. Only 7.2K, but even 5 years ago, 10K didn't deliver that transfer speed from what I remember.
I'm getting about 100MB/sec from 3.5" Samsungs, WDs and Seagates today - but you're right according to these 4 year old benchmarks: http://www.storagereview.com/western_digital_caviar_blue_1tb...
I guess the configuration I'm benchmarking with, and the type of load, which is basically streaming, but from a journaled-but-otherwise-standard ext4, slows me down a little. But the convenience and standardness of this setup is worth more to me than a factor of 2 in performance (that's not my bottleneck at the moment).