Pros/Cons of Using Mixed RAM Sticks?

I recently decided to upgrade the RAM on my old laptop, a 3.5 year old Gateway MX6650 running (according to Gateway) 1024 MB DDR2 (2 x 512 MB) SODIMM, that my sister owned before me. I promptly went out and bought a stick of Patriot 2GB 200-Pin DDR2 SO-DIMM DDR2 800 (PC2 6400) from newegg, thinking I could benefit more from using 2.5GB RAM rather than buying 2x1GB and tossing both old sticks.

In the days since I've read all about the benefits of dual channel RAM and the detriments of using RAM with mixed speeds, and was planning on asking some helpful tech people (ie: you ) about that. But then I found out that my laptop is only upgradable to 2GB anyway , and although I'm still really curious about whether my 2.5GB RAM would actually have been slower than just the 2GB if anyone wants to answer, it's become academic.

Could someone tell me instead how much of a difference there is between 2x1GB vs 1x2GB? This is a mistake I could correct cheaply, but if it's only a small difference that won't be detectable in daily use (I don't game extensively), I won't bother.

Thanks in advance for your help!

I don't think you would be able to tell the difference.
Dual channel may help a little. Think low single digitsat most.
More ram helps much more.
Mixed ram may not be good, some motherboards are very sensitive to that.

Thanks for the responses. I almost always do this sort research before a purchase, I think I got too excited at the prospect of this computer not running like molasses and bought too early. I'll be putting the 2GB stick on ebay I guess and looking for a 2x1 set.

If you don't mind though, what is interleaving? And is dual channel not standard on motherboards? Or maybe it's become standard more recently than this laptop was built...