Deciphering Hynix RAM options for Westmere 6-core

I was looking into 8 GB RAM options for new new refurbished MacPro5,1 3.33 GHz.

Hynix has no less than 8 different 8 GB DIMMs that fit the bill!

I added notes based on what I saw on an Intel® memory configurator site:

http://serverconfigurator.intel.com/configure-memory.aspx?id=Mzk4MCMxLDM4NDQjMg= =&ShowNavigation=false

Name Notes

HMT31GR7AFR4A-H9 *Not 8 bank; older (2009); low-voltage(?); 512x4; has thermal sensor*
HMT31GR7AFR4C-H9 *Not 8 bank; older (2009); normal voltage; 512x4; no thermal sensor(?)*
HMT31GR7AFR8A-H9 *Not 8 bank; older (2009); low-voltage(?); thermal sensor(?)*
HMT31GR7AFR8C-H9 *Not 8 bank; older (2009); normal voltage; thermal sensor unknown(?)*

HMT31GR7BFR4A-H9 *8 bank; newer (2010); low-voltage(?); 512x4*
HMT31GR7BFR4C-H9 *8 bank; newer (2010); normal voltage; 512x4; has thermal sensor*
HMT31GR7BFR8A-H9 *8 bank; newer (2010); low-voltage(?); thermal sensor unknown(?)*
HMT31GR7BFR8C-H9 *8 bank; newer (2010); normal voltage; has thermal sensor*

That's quite a variation! I know that Apple requires the thermal sensor, so that eliminates some.

(The 4A/4C-H9 vs. 8A/8C-H9 seems to be DIMM size, not 4 GB vs. 8 GB - these are all 8 GB DIMMs.)

The Intel® page says the "low-voltage" ones can only be used with Xeon 5600 CPUs; of which mine is one. True? I haven't seen any reference so far that says "low-voltage" DIMMs can be used in a Mac Pro.

There's quite a difference in price between the "A"FR and "B"FR models, too - anywhere from US $30 ( SuperBiiz ) to well over $100! What's funny is that it's the older "A"FR series that is the more expensive. I have no idea why???

Yes - I know I'm overthinking this 🙂

But it's still a bit confusing ... I am leaning towards the HMT31GR7BFR4C-H9D7 model because it's got the thermal sensor, it's newer, it's (inexplicably) cheaper, and I can actually find it for same on-line.