Around July 2003 I bought a WD2000JB (-00DUA0, s/n WMACK...), made in July 2003. I measured the transfer rates with both WinBench and H2BenchW, and got similar results for both benchmarks, and using two different controllers (ATA/100 and ATA/133). For example H2Bench reports read max/avg/min as 55629/45070/30051 KB/s. The write rates are almost the same.
A couple of weeks ago I bought another, thinking to make a RAID-1 (mirrored) pair. It had the model-number suffix -00EVA0 and a/n WMAEH..., made in Nov 2003. I also measured its performance and found it to be about 20% slower: 45328/38792/27714 KB/s; again the write rates are nearly the same.
The measurements were made under the same conditions -- the only disk on a controller, configured as master, under Windows XP in safe mode. (For the first disk I had tried measurements with two different controllers, and got essentially the same results).
The numbers for the first (faster) disk seem to match what I've seen here and elsewhere on the Web.
Has anyone else found newer drives to be slower? I sent the results to Western Digital support, and the answer was that "they are both in spec" so not to worry. I have returned the slow disk for a refund, but would still like to find another like the original. The disks currently in stock (at Fry's in California) are mainly very new, Feb-Apr 2004. Any idea how they'd be?