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Western Digital WD5000KS Reviewed
Spinnerbait writes "Hothardware has a review of the Western Digital WD5000KS, a member of Western Digital's Caviar SE16 family. It's a 500GB SATA 3Gb/s drive, features a 16MB cache and a 7200 RPM spindle speed. WD's Raptor line, with their 10k RPM spindle speed, may have won the overall 3.5" desktop HDD performance crown, but they don't win any capacity battles. That's where the WD5000KS comes in. Up against Seagate's finest, the Barracuda 7200.10, the half-terabyte WD5000 holds strong performance metrics."
http://www.hothardware.com/printarticle.aspx?artic leid=847
The answer should be obvious: To get higher numbers.
For "Buffer to Disk", there is significant overhead caused by encoding the data with error correcting codes, sectorization, etc. This can make it use 10-15 bits per byte, with the expected performance of a 748 Mbit/sec drive being around 60-70 megabytes per second at the beginning of the drive (where rotational density of bits is highest), with 30-40 megabytes per second at the end.
For "Buffer to Host", MBytes/sec is the traditional measure. The overhead on SATA is better than traditional PATA (where for UDMA133 it's about 50%). The raw wire speed of SATA-II is 3.0 Gbit/sec, so advertising 300 Mbytes/sec is beyond realistic - even the theoretical maximum is probably less due to overhead. In benchmarks the drive achieves 180 Mbytes/sec buffered reads.
70 degrees!? Assuming your drive is reporting correctly, you need to do something to cool that down - fans, adjusted airflow, passive cooling, etc. Anything over 40 degrees cuts down drive life and anything over 50 degrees is just asking for trouble. Peaking at 70, I'm surprised your drives are still running at all.
This drive has also been reviewed by SilentPCReview for those of us, who are more interested in noise than in performance. Another 500 GB Caviar model, the WD5000YS, was covered by StorageReview -- IIRC, the differences between those two drives are in the firmware.