The 6230 was disgustingly fast in the UI. I've used 6682, N80, N73, E62, and N75 since the 6230 came out. The 6682 and E62 were SLOW. N80 was faster, N73 was right around the same speed as the N80. The N75 blows them both out of the water in terms of quickness. Not equal to the 6230, but pretty damn close.
Also, one thing I've noticed is that if you reduce the amount of icons (be it folder or app) on each menu screen, the whole thing seems to move faster. I.e. I used to have 2 extra lines of folders and apps on my main menu. I've since moved folders and apps around so that there's only the 12 showing that show when you first enter the menu. Same for any folder. And I can notice a slight different.