Asus P5AD2 Premium & DDR2 RAM configuration

According to Crucial:

While performance gains from Dual-Channel Chipsets aren't huge, they can increase Bandwidth by as much as 10 percent. To those seeking to push the performance envelope, that 10 percent can be very important.

So the next time you come across a product that's touted and sold as Dual-Channel DDR, know this: It's simply two DDR Memory Modules, packaged and marketed as a specialty product or a must-have "kit."

If indeed you have a Dual-Channel Platform and you want to take advantage of the performance gain it offers, our advice is to opt for high quality and service over expensive packaging, and simply purchase your DDR Memory in Pairs. However, be very careful to order Two Modules with the exact same Specifications; the Modules must be identical to each other to perform correctly."

Dual Channel memory configurations will provide increased performance over Single Channel configurations. Note: Memory channel speed is determined by the slowest DIMM module populated in the system.

Rules to Enable Dual Channel Mode
To achieve Dual Channel mode, the following conditions must be met:
1. Matched DIMM configuration in each channel
2. Same Density (128MB, 256MB, 512MB, etc.)
3. Same DRAM technology (128Mb, 256Mb, or 512Mb)
4. Same DRAM bus width (x8 or x16)
5. All either single-sided or dual-sided
6. Matched in both Channel A and Channel B memory channels
7. Populate symmetrical memory slots (Slot 0 or Slot 1)
Note: Configurations that do not match the above conditions will revert to Single Channel mode.



However I’m in need of a little clarification.

Ultimately I want to have 2GB total and gain the added 10% of bandwidth.
Simple answer would be to buy 2 1GB twinned banks.
But I'm anxious and I don't want to wait to save up the extra cash required for 2GB I settle for 2 512 twinned banks. If I decide to save some money by going with 2 512 twinned sticks as opposed to 2 1GB twinned sticks and at a later date upgrade to 2GB by adding another 2 512 twinned sticks what is the possibility of the motherboard reverting to Single Channel mode or losing out on performance when comparing the 2 1GB twinned sticks against the original pair of twinned 512 added to the new pair of twinned 512 seeing as how the old and new pairs were not twinned to each other at the time of manufacture?

Thank you