Slow playing is harder than most people think. Phrasing ("breathing" at the right place), vibrato, creative bending and note choice are much more vital to keep the solo interesting. Funny how many of the anti-shred advocates who play with "feel" tend to miss the mark, choosing instead to fill the solo spot with noise.
There are some great slow solos out there, many of which are played at brisk tempos. "Achilles Last Stand" is an excellent example of this. Blackmore was great at slower playing too.
Of course, the opposite is true too. Nothing like a drop dead killer note blazer during a slow song, like AC/DC's "Ride On".
Cy