ah the old "it just feels better" thing. That, along with the "in games the Phenom feels smoother" are the only arguments I ever hear :/
Yea, it used to make me laugh too, now, I am by no means giving any kind of real credence to such assertions. But, before I upgraded to an I5 (at 3.6GHz) set-up I used to have a Phenom II 940 BE (at stock 3GHz) both had/have 4GB of ram.
Now unsurprisingly when I upgraded to the Phenom II at the start of this year, I switched from a duel core C2D E6600 run at 3GHz, and I certainly found the Phenom II to be 'smoother' I could tell the difference between them in certain situations even when a quad wasn't much if any 'apparent' advantage over a duel core. I just put it down to an improvement in technology really, and the fact that I had twice as many cores as before.
Now interestingly, I have noticed, only really playing Supreme Commander though, a difference in the I5 and the PII, the PII was (I swear) smoother. I can't explain it really; the I5 is faster clock for clock let alone when it has a 600MHz advantage ...both chips have the same number of cores, neither has hyper threading. All I can conclude is, the cache setups are responsible for this, either that or I'm just imagining it (but I don't think so).
The I5 is a faster chip than my old PII, no doubt, in real usage I hardly notice the difference actually, but when I run benchmarks I certainly do. But for reasons I can't explain, in Supreme Commander Forged Alliance, the old PII certainly did offer a 'smoother' experience.
I don't think I would base a cpu purchase on this, I mean it's highly situational at best, and is usually considered to be a line touted by AMD die-hards clutching at straws. I'm not one of these people, I've sold the PII, I use an I5 now (I've never been a fan-boy type anyway) ...but yea, the PII, under certain circumstances was smoother, I'm pretty sure of that. Although I didn't believe it at all when I had one, but then I couldn't make a direct comparison to an Intel quad at the time.
I have noticed similar behaviour in Warhammer 40K: Dawn of War 2 when things get intense, but not nearly so obvious as SC:FA, it's something on the edge on my hardware spidey sense there. I haven't noticed such behaviour when just plain multitasking, then again I don't do really heavy multitasking all that often, I do run 2 Eve clients simultaneously and a Skype webcam feed, that's about as heavy as my multitasking gets.
Take what I have said with a grain of salt, or 20 …but that is what I have experienced, having made the switch from the Phenom II to the I5 on release day.