Ok...
Prior to my e6700 and 8800GTX I had a D805 and a 7900GT.
At first I had these running on an ASrock 775DUAL-Vista with 1.5GB DDR1 (1GB+512MB), then I went to 1GB DDR2 (Single DIMM) then to 2GB DDR2 (two DIMMs) then to the Asus P5W DH I have now with the same Gfx card and RAM.
In Summary:
1. Asrock, DDR1 1.5GB,
2. Asrock, DDR2 1GB,
3. Asrock, DDR2 2GB,
4. Asus, DDR2 2GB.
I can tell you that while there was a small jump going from the DDR1 to the DDR2 on the ASrock board, the jump from the ASrock board to the Asus board was MASSIVE, even with both using DDR2. I could score in 3Dmark 06 with my Video card at stock speeds more on the Asus board than I could score with it at 740/1400 (almost 80% GPU overclock) on the ASrock board.
I also tried limiting the Gfx card to x4 mode on the Asus board, and it STILL performed much better than the ASrock one. Added to that it allowed MUCH better CPU overclocks than the ASrock board.
In short, I think the limiting factor was not the PCIe x4 or the DDR1, (although the DDR1 did suck, I got about 15% switching to DDR2) but the crappy VIA chipset motherboard. The Intel chipset boards simply perform much better, and especially for this scenario where you have such an overclockable CPU, will serve you much better.
If I were you I'd go for a P965 board and 1GB of DDR2-667 in a single DIMM with a view to adding a second DIMM later when I had the cash. Or even 2x512 with a view to adding another 2x512 later, the difference is minimal.
The 775DUAL-Vista has an FSB limit of about 280-290, this would take your e6300 to 1.96GHz - 2.03GHz, a very small overclock. The ECS board seems worse from the BIOS options. A P965 would give you at least 400MHz, or 2.8GHz.
If you go the 775DUAL-Vista route you'll only be looking at replacing the thing in 6 months when you have switched to DDR2 on it anyway.
You could probably even sell your 2GB DDR1 for enough to buy at least 1GB of DDR2, or use it to keep your old system going and sell that....