I think it's probably due to power gating..
I've had this problem on many laptops, where the aggressive power plan (windows Balanced) downclocks the cpu and possibly the chipset, this raises DPC latency.. causing stutters..
But if I put it in High performance mode, everything becomes super smooth..
I think that may have been the case if your i3 was feeling slow..
vs the i5, the 2540m also has 3.3ghz turbo, and it can actually turbo both cores to 3.3 for a short while, / when temperatures allow it. (depending on manufacturer of laptop)
I get what you are saying, however, that's not the case.
All were fresh installs using identical power plans, balanced as well as performance mode, all used Win7 configured the same as well.
Yes, the I3 did smooth out some in performance mode, but it was still garbage, while none of the others required this. The I3 was swapped out for the 2540 without a re-install just to see if it made a difference, which it did.
Given identical memory, as I said, you would be hard to tell on a day to day basis which was which, other than the I3. Could you tell in something seriously demanding long term, probably, but 99% of the time, you wouldn't know the difference. It is possible that the newer processors simply needed more memory to wake up, it wouldn't be the first time I've seen that, but I don't have 8 gigs I can put into the p8500 to do a comparison. Don't get me wrong, I'm not saying every C2d is better, but the higher end ones, can still hold their own.
I would still rather have, and do recommend the CI series over the C2d, but I wouldn't say it's no longer worth using, especially when Intel is shipping low end C2d's repackaged (Pentium) and AMD has only just exceeded high end C2d performance with the A6 and A8 series.
Actually, the #1 reason to get X201 instead of X200 is the graphic chip. Drivers work slightly better, and esp. hardware video decoding works out of the box with Intel HD.
I agree, with you, it's the best reason, but is it worth 50% more money? probably not.