Some people will argue that single channel is only "5%" slower than dual channel... but from my experience it makes for far longer loading times and generally less responsive system.
Your going to lose a bit on a 32bit system but personally I'd rather have a nicely rounded out dual channel and as much of 4gig as I can use.
Incase it wasn't clear from my earlier post - you have to bare in mind that the 1066 and 667 clocks stated are the DDR rated speed... (double data rate) and 333MHz as shown in CPU-z is the base frequency of the RAM which you have to double to get the DDR rated number.
The FSB is quad pumped - so if you set it to 422MHz (like it is now) the effective speed will be ~1690MHz. However, the effective RAM speed is only doubled (due to DDR) - so it would run at 844MHz if you set the base bus clockspeed to 422MHz and used a 1:1 divider.