different size RAM affecting performance

I currently have 2x1GB sticks of RAM. If I add 2x2GB sticks (total of 6GB) that are the same brand, series, have the same latency, timings, frequency, and each pair is inserted to be dual channel (same color slots or whatever), will the difference in capacity per stick alone (1GB vs 2GB) affect the cumulative performance and prevent the benefits from dual channel?

 

What operating system are you using? XP, Vista 32, Vista 64?

I think Vista 32 has a limit of 4 gigs. Vista 64 is much more than that.
XP usually works fine with 2 gigs, depending on what intensive software you may be using. Hard core gamers, Video editing, etc., could benefit from more than 2 gigs in XP. For light users, like myself, 2 gigs is a waste in XP Pro SP3. 1 gig is probably enough. Bazza

 

I meant performance independent of what operating system is being used. I'm just asking if, assuming I'm using an OS that supports at least 6GB, memory performance is affected by a difference of capacity alone, and if two 1GB in one dual-channel and two 2GB in the other dual-channel will affect dual channel in some way because of their different capacities, or if one dual-channel pair doesn't affect the other and relies on their own pairs.
This upgrade won't happen for a while, I was just curious for future reference.

 

I know what OSs support how much RAM
I know what type my motherboard supports and how much it can hold
My question doesn't involve either of those factors.

Two 1GB sticks in dual channel formation
Two 2GB sticks in dual channel formation
My question is whether both dual channel formations will be possible on capacity alone (1GB formation vs 2GB formation), or if dual channel can't be done if the second dual channel formation contains RAM of a different capacity.
Will the two 1GB sticks be considered dual channel, and will the two 2GB sticks be considered dual channel, or will performance be affected by the system noticing that the other dual channel formation doesn't have RAM of the same capacity (ie 2x2GB dual channel not working because the other dual channel formation isn't also 2x2GB)? Or does it not care just as long as there are two identical sticks of RAM to be considered a dual channel formation?

To reiterate and possibly make things simpler, let's say I have two 1GB sticks in dual channel slots, so the system recognizes it as dual channel. Then I decide to put two 2GB sticks into the other dual channel slots (without moving the 1GB sticks). Would the two 1GB sticks no longer be considered dual channel because two 2GB sticks are present?
(everything is exactly the same between the RAM sticks, the only difference is 1GB vs 2GB...yes, OS can support it, motherboard supports the total amount, all that stuff)

Maybe it's just a ridiculous question, but I just wanted to make sure.