Here are direct links to your images (no ads, banners, etc):
The read benchmark graph is a monotonically decreasing curve because there are more bits per track out the outer zones than at the inner zones. The usual ratio between max/min data rates is about 2:1.
Compare your HD Tune results against these:
Your drive’s burst rate, 193.8 MB/s, reflects the data rate into and out of the drive’s cache. Since SATA-2 specifies an interface rate of 300MB/s (= 3 Gbps), and SATA-1 is 150MB/s, this tells us that the drive is operating at SATA-2 speeds. UDMA Mode 6 (Ultra ATA/133) is limited to 133 MB/s.
As for your cache question, the standard ATA Identify Device command only allows for reporting a maximum cache size of “32MB - 512 bytes.” This equates to a maximum value of 0xFFFF for word 21 in the ATA Identify Device data block. Therefore your drive reports 0.
Detecting Buffer or Cache Size in ATA Hard Disk Drives:
Your RPM question is a good one, though. WD obfuscates its RPM specification by referring to it as IntelliPower. The drive actually reports 0 RPM. However, you can see the actual RPM in HD Tune’s access time graph. Notice that the width of data points is about 11msec. This corresponds to the time for one revolution at 5400RPM.
What disturbs me, however, is the large discontinuity at about the 550GB mark. This suggests to me that the drive is having difficulty reading beyond about the third zone. The separation in the data points appears to correspond to an additional revolution, suggesting that the drive is performing read retries. I’m wondering whether this is symptomatic of a miscalibrated head.