Demonoid

Definitely yes! Just some of my favorites -

Camel - Reflections/Captured(It's two separate tracks)
Gong - Expresso
Goblin - Aquaman(Pretty much everything by goblin actually)
Riverside - Reality Dream II(Include Reality Dream I & III as well)
King Crimson - Sailor's Tale

Then there's Frank Zappa, Mahavishnu Orchestra, Mike Oldfield, Whether Report, Rush(La Villa Strangiato comes to mind), more king crimson, lots of Italian bands, Ozric Tentacles, Tangerine Dream, Gryphon etc.
The list is just endless and I'm too lazy to name all the exact songs
There's also a "Post-Rock" genre which is more or less instrumental.

But are prog instrumentals the pinnacle of the art?
Well, not exactly, but prog. bands do tend to do more instrumentals and are always bound to be better.

is longer better?
Depends on the song.

Edit: There are a lot of Metal Instrumentals as well that are really good, but even those bands do tend to be called "Prog".(although there are some which aren't)