Originally posted by: blackrain
I have seen a few online discussions that the difference between cas 2 and cas 2.5 is almost negligible (maybe a 3-4% difference at the most)...is that true in every case? as far as prices, it seems like there is only a $10 difference.
as far as my situation goes, it seems like I took one step backward. In thinking that I was getting something better (3200 v. 2700) I incidentally downgraded myself from cl 2.5 to cl3 (the PNY memory at Best Buy appears to be cl 2.5) I have to return the Kingston memory regardless because they gave me registered memory...just wondering if I should try to get the PNY memory back or should I get CL 2.5 3200 online, or even CL 2 3200 online.
Side question: As you can tell from this thread, initially I didn't really understand how complicated memory is today. I was trying to go cheap for now and add another stick later. But I sense a problem in doing that. Memory modules from different manufacturers seem to have different timings. If I buy one 512 mb CL2.5 stick right now and a second one later with different timings, they probably aren't going to be in synch. It just seems like I should buy a dual channel kit or a 1GB module today instead of buying one stick now and waiting to add another one later. Am I overcomplicating this? Probably
Edit: How does one 1GB module compare to 2 512mb modules in dual channel? Is there any reason to get one versus the other (my board has dual channel DDR)
A lot to clarify...

The difference between a Cas of 2 and 2.5 is indeed hardly noticeable... Where it may make a difference however, is in the overclocking department... RAM that has a CL of 2 @ 200MHz will, almost certainly, be pushed further than RAM with a CL of 2.5... Not because it has the lower Cas, but because of the fact that you can up it twice... If your RAM can't go higher than 220MHz @ CL 2, it will probably go as high as 240MHz (just numbers), once you upped the CL to 2.5...
If you raise it to 3 (the limit of most mobo's), you could maybe even hit higher... The CL 2.5 RAM can only be upped to 3... However, by buying sticks with a CL of 2, you are buying high-quality sticks... Manufacturers use better memory chips for these in comparison with their "value" lines... Which makes sense...
The PC2700 memory may have a lower latency, but it will lose to the Cas 3 PC3200 because of the lesser bandwidth... There's a point where low latencies lose to high speeds... However, the RAM sticks are almost certainly identical to one another... The PC3200 one can probably be lowered to a Cas of 2.5 at PC2700 speeds... Don't see it as "worse" memory... Buying your memory online is always the best outcome, as prices are much lower than in retail stores...
Memory sticks from different manufacturers don't often have different timings... Fast Corsairs usually have timings like 2-3-3-6, so do others like OCZ and Crucial... The memory modules are made by independent memory manufacturers, such as Hynix, Winbond and Samsung, and these are used throughout different brands...
Modern motherboards know how to handle different sticks, but mostly it's wiser to just stick (no pun intended) with the same brand and model if you want to add sticks later... If you buy a stick today, and you want another one tomorrow, then that should be fine, even for dual channel... If the timings are different, modules will be "corrected" by the mobo so they can run fine...
If you make sure that the module you'll buy within some months is completely the same, then you'll have no problems whatsoever...
A single 1GB module will be slower when compared to dual channel configs of course... However, the difference will not be that apparent (look at Socket 754 versus Socket 939) for gaming, but only in memory-dependant situations... The only reason I can think of, is not wanting to have problems when occupying all four memory slots...

If you want 2GB, then IMHO it's better to buy a 1 gig stick now, and the other one later, instead of 4x512MB... You could however buy a dual channel kit now, and sell it when you want to upgrade to 2 gigs... That would be even better...
Hope I helped...