Interesting. Back when I switched my Firefox builds from Core2 Duo T8300 @ 2.40 GHz + spinning disk + OS X to i7-950 @ 3.07GHz + SSD + Ubuntu, GUI responsiveness during Firefox build went from OK to bad. Canonical's support suggested getting a second computer as a build machine.
May be the machine too. I "feel" my Xeon desktop and my i3 laptop degrade more smoothly than the i7 laptop. It's entirely subjective, of course, but when I torture the machines the i3 go from usable to uncomfortable while the i7 goes very usable to unbearable. The Xeon goes from very usable to usable. Could be the i7 throttling more heavily from thermal issues.
