This discussion is going too off topic. But since you have
raised the issue, let's finish it off quickly so popo can decide quickly
First of all, the system bus frequency of my c2d system and Popo's Q6600 is 1066MHz. So you should not think that the memory speed will be limited to 300-400MZ. That's because it completes multiple data transfers per clock cycle. There are many good mainboards for the Q6600 cpu. Let's consider the Intel DX38BT
. As you can see, it supports DDR3 1066 and 1333 MHz RAMs, and can perform at full speed according to the CPU FSB Speed, in this case 1066MHz. It's nothing new - intels "quad pumping" has been here for quite some time. Otherwise, why even consider 800MHz DDR2 RAMs at the first place if all you"ll get is 677MHz? Simply doesn't make sense, does it? You might ask, if popo's FSB is 1066MHz, then why opt for faster DDR3 modules? That's for time-proofing for the next couple of years or so, if she does go for a newer system. The PSU, RAM, SSD (if any), HDDs, optical drives etc don't really need upgradation every year isn't it? Since we agree that faster, more RAM can make quite a difference to her photoshopping experience, so my suggestion was to get a mobo and the RAMs, which she can enjoy for quite some time for what she does. And if in a few months or a year she does get a new system, she would be able to use these RAMS just fine with a faster cpu/mobo with better bus speeds etc. And fsb:memory-speed ratios vary across system to system; intel does support non 1:1s. The bottleneck of FSB (which intel is trying to overcome with the new bus architecture for i7 cores) was never an issue for AMD. They use direct link between the cpu and the memory interface.
I repeat again, nobody can stop you from buying anything, but tell me honestly, would you at all consider any upgrade (other than memory) if all you did in your pc was a little photo editing? I mean, no 3d at all. The upgrade from gts 250 to gtx275 would be totally useless, even if you got it for free. For cs4+plugins, popo's current system is just fine. If she upgrades right now, she will have to pay a LOT more that what it might cost her a few months later.
The cooler is always a good thing to buy. But what if your card doesn't heat up that much at the first place? Well, GTS 250 does that job perfectly well. I am not sure the 275 will be as "cool" or silent. My mood varies, but will popo ever frag us in a MMOFPS? I really doubt that...