One of the tricks in the blues rep. is to use the minor pentatonic over the major chords. For instance, when playing over E major, A major and B major (a I, IV, V progression) in the key of E major, use the e minor pentatonic. Stevie Ray's tune "Lenny" from Texas Flood is a perfect example. The basic chords of the verse part are E and A major, but most of the lead guitar melody is based in the e minor pent scale. That's one of the standard ways to get the "blues tension."
Gilmour does this, I guess most of the big dogs do it. Trick is, you can throw the major arpeggios and broken chords into it as well. They both work, and together they are an INCREDIBLE sound! Alot of that punch I mentioned earlier comes when he has played several riffs in the e minor scale, but when he plays over the a chord, for instance, he'll occasionally throw in an A major arpeggio. Adds that perfect element, just changing the c in the a minor chord to a c#, from the a major arpeggio. But he won't stick to just the c#. He'll use them both, sometimes in the same phrase. Same thing when soloing over the B major chord. Still the e minor pentatonic, but he'll throw in the d# from the B major arpeggio, and when on the V chord of any progression, also emphasize the 7 note, to really bring out the dominant 7 blue feel.
This is the easiest way to add a little "outside" playing to the pure pentatonic, without actually changing scales or keys.

Does this help with your original question?
Best wishes,
Michael