Interesting. Can you clarify this more? Do you mean "bank" or do you mean "chip"?

I don't mean "chip" (I don't even mean "module"). Some people use the word "channel" instead of "bank". Yet others call this an "interleaved" memory subsystem.

These chipsets basically have two independent memory interfaces on, so they can get 3200Mbytes/sec (for DDR400) out of each of them. The chipset accesses them alternately, so the CPU effectively sees a single 6400Mbytes/sec memory subsystem.

Is each slot a bank, or is each pair a bank?

That depends on your motherboard; it should say in the manual whether or not you have a dual-bank memory controller, and, if so, which DIMM slots belong to which bank. If you have four slots, it's not at all likely that each one is in its own bank -- only the biggest-ass chipsets have four memory banks.

If each pair was a bank instead of each slot being a bank, would I get better performance if I plugged them in thus?:

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Yes, if that's indeed the layout. Some chipsets (e.g. Serverworks 3LE) won't boot the machine unless the two banks are matched (much like the old days of SIMMs being installed in pairs or fours); other, more consumer-targeted ones, will boot with mismatched banks but operate them as a single bank.

Peter