When overclocked, N900 has more raw power, but UI is more sluggish, what with lower support for GPU, worse GPU, and bigger screen (twice the pixels). Plus, CPU is slower as I understand it from N900-stock?

However, whether a phone is slow or not is not very important when used. It's not a PC, it should not be treated like one. It could have a 3 GHz CPU in there, if I have to way 2 full seconds for the Phone to come alive I'll feel it is sluggish.

Besides, Symbian is lightweight compared to M5, with a simpler UI and that accounts (I feel) for the speed difference. If E7 could run M5, I'm pretty sure N900 would feel faster.

What strikes me is that E7 almost never swaps. Apps seem to take less RAM and the OS could be smaller in RAM too, or the on-board storage could be faster. It doesn't pause as much when exiting apps not does it choke as much as N900, especially since N900 has start and close animations, making it more visually vulnerable to slowdowns. Still, After playing a 3D flight simulator, and exiting, phone is responsive almost immediately, especially if it cheats a little and keeps desktop and menu loaded in memory. Cheat or no cheat, there is nowhere to go but desktop and menu for at least 2 seconds, so it feels fast.

Since there are few cross-platform direct-translate apps, it's hard to compare. It's a general feeling, at least partially because of graphics (not seeing bitmaps being painted is a plus).

As for filled storage, no wonder it slows down. Performance of flash gets severely diminished with increase in use, fragmentation, etc. Also, some software out there are written by people who deserve a kick in the groin. Inability to let user choose refresh rate for a widget is a bad, bad idea. Fortunately, there are plenty alternatives.