Will upgrading to Lion boost performance and responsiveness?
Solution 1:
All of the press / industry coverage is focusing on the huge usability changes (and that mirrors the marketing that Apple is doing).
Some notable exceptions are the new Safari which runs some benchmarks like web app and JavaScript significantly faster.
The major changes under the hood speak more to security, sandboxing and plumbing the new multi-touch interface, encryption, auto save, auto revisions rather than speed.
It is too soon to tell if speed is much better, but once people adapt to the changes, the idea is we will be much more efficient with the computer waiting for us less than the other way around. I would expect your experience with the hardware you mentioned to be a minor speedup in pure numbers but a major speedup as your brain becomes free from worrying about saving, window management and revisions (assuming you adapt to the changes and like them)
I get the feeling that with mission control and full screen apps, that the UI is incredibly fluid and optimized but I'm running on some faster macs than yours.
Fun times, huh?
Solution 2:
I have definitely noticed an increase in the speed of safari and Xcode, and this article seems to confirm that others have had the same experience. Also, everyone else that I have spoken to has noticed a speed boost as well in many applications. This discussion also proves that isn't just me and select friends:
http://forums.macrumors.com/archive/index.php/t-1168519.html
Though I cannot cite any numerical proof, it is noticeably faster for me.
Solution 3:
I have a MacBook with exactly that configuration. Lion is de-facto faster in some areas (World of Warcraft, for instance, runs 10-15 frames faster), but may "feel" slower in others (e.g. opening a window sports a new animation and gives the impression that it's delayed a bit). This "feeling" is of course not specific to that machine. Anyway, Lion is certainly not slower than Snow Leopard on a Late 2008 MacBook.
Solution 4:
I have a 2011 quad-core i7 15" MacBook Pro with 8G RAM, and Lion is noticeably faster than Snow Leopard in all areas.