I'm a commercial photographer and use PhotoShop incessantly. When I first
assembled this computer (P4 2.8, Gigabyte 8KNXP v1 non-Ultra), I installed
1gb of RAM, a matched pair of Kingston CL3 (KVR400X64C3AK2/1G)--and later
added another 1gb. I noticed no difference in performance between 1gb and
2gb, except that now I can load dozens more high-res photos into PhotoShop
without exhausting RAM and calling upon virtual memory (swap file). It is
rare that I load this many files simultaneously, and if I had to do it again
I might settle on only 1gb and load only 50 files at a time rather than 100,
taking the extra $200 and applying it somewhere that would reap more benefit
(see below for a suggestion).
As for the difference between CL2 and CL3, I doubt if you'll realize any
practical difference unless you gain enjoyment running benchmarks, and even
then you'll see only a small difference. What will make a major difference
is installing dual-channel memory on a mobo that supports it. The bandwidth
will be double that of single-channel, although that doesn't translate into
double the overall computer performance. The RAM is fast anyway, and if you
double it you may not even notice the increase.
What did make a difference here was upgrading from a standard PATA harddrive
(Maxtor DM9, 8mb buffer) to a WD Raptor SATA. The drive will slow you down
more than any other item, and these new 10k RPM Raptor SATA's are as fast as
you can get short of high-end SCSI. I have the 36gb used as C:, and the
newer 74gb are even faster. I don't store photos on C:, rather on D: (the
Maxtor) and two firewire drives.
I'd install 1gb of CL2 RAM and buy a 74gb Raptor HD for the $200 you'll be
saving. That would be the best application for your money, IMHO. If you
store photos on your boot drive (C

, you may need to think again about the
Raptor since 74gb is currently the largest available, but my C: routinely
has only about 15gb on it, as I only use it for working folders for photos.
As soon as I finish running them through Nikon Capture, editing in
PhotoShop, and delivering to the client, I move them to much larger archive
drives.