Thanks everyone for the feedback.
The HSF are made by Ajigo. You can find more information in their web page and some reviews in Frostytech, although none are too detailed and it's difficult to find exactly what HSF is the one you have.
I found two articles at FrostyTech but they were both for Socket A coolers. But thanks to your reference to "Ajigo", I think I found the right one here
(it does look very similar to the ones in the FrostyTech review).
The RPM range that people have reported is consisted with the product literature
(I assume the 1000 RPM figures are after additional fan control has been added). One interesting tidbit is that it retails for US$36 from the Ajigo store--only a few dollars less than a Zalman 7000 series.
Having found the model number I was able to find quite a number of reviews in which it's compared with fancier coolers. One thing they suggest to me is that, while the stock cooler is hardly in the same league as the best third-party heatsinks, it is somewhat let down by a crappy 15mm fan which doesn't move much air except at very high RPM.
Given that that I plan on getting one of the cooler CPUs (Sempron 3100+ or 90nm Athlon 64) and am not obsessed with running my CPU at the coolest possible temp, I suspect this heatsink has the potential to keep me happy. The key will be replacing the fan. rperezlo mentioned he's using a no-name 80mm attached with one screw that's doing the job for him, though I'd prefer something neater. 70mm fans don't seem all that common where I am, but I did find this one
. At 3000 RPM, it's rated at 27.5dBA and moves 32 CFM, compared to the Ajigo's 28dBA moving 21 CFM. With that fan's speed reduced, it may be an acceptable and inexpensive solution.
Still unconfirmed is whether the Sempron includes this particular heatsink. Anyway, I'll be putting my new system together in a couple of weeks, so I'll report back on my experiences then