I find IE8 slow to me, and IE7 even slower. This is after having tons of tabs opened as I tend to have. And there's quite a delay when opening a new tab too, which doesn't happen with Chrome. (comparing the two, since they both open a new process for each tab)

Memory usage? After having tons of tabs opened, Firefox is better for me. Otherwise is IE + IE + IE + IE +...+ IE (same with chrome), although yes, one tab won't crash them all. This is in "rush hours" and for performance, Firefox also wins for me in "user experience" as opposed to benchmark (chrome may too, but I miss ma'lovely addons.. T_T).