Super Breaks compilations on Ace - where next?

I really like this series, Volume 3 of which is just out. I've also got all 4 of the Harmless series "The Breaks". Obviously, it's the beats that first attracted me, but it's the songs and performances that really stick in the mind.

So what should I get next? I'm more interested in the pop end than the jazz end of this soul spectrum. A Stax singles box set looks like a no brainer. Other labels that crop up time and again on Super Breaks are Volt, Eastbound, Westbound, Enterprise, Fantasy, Prestige and Spring. The Atlantic/Atco and Cotillion labels also look very interesting. CD recommendations appreciated.