Best mix/match DDR2 in Dual-channel banks?

I find myself not really understanding what the best/optimal memory config is for this little rig based on the available parts I have laying around.

this is an older Dell Dimension 4700, Intel 915G chipset, Pentium 4@ 3.0GHz.
Dual channel memory, four slots total. 800mhz FSB

I have 2x1GB PC2-6400U-666-12-ZZ, 2x256 PC2-3200U-333-10-C1, and/or 2x256 PC2-4200U-444-11-C1 to mix/match.

The first question I have is: how do I know which bank is bank '0', and does it matter? the banks [0, 1] are color-differentiated physically. [thankfully]

Second, which config will deliver the best performance:
A - Dual channel, 1GB each in first slot of each channel [or does it matter which slot as long as its dual channel? Total=2GB

B - Dual Channel, 1GB each in one slot of each bank, pls one each PC2-3200U-333-10-C1 256mb in the 'other' slot of each channel/bank. total 2.5gb

C - 1GB each in one slot of each bank, plus one each PC2-4200U-444-11-C1 in the other slot of each bank. total 2.5gb

?

I'd stay with the 2GB of DDR2-800 (PC2-6400) only. All of the RAM will run at the frequency of the slowest RAM. It's not worth the performance hit to only add 512MB.

That assumes that the PC actually runs DDR2-800 at its nominal frequency.