subwoofers: the bigger the better?

Hi guys, I wonder if a bigger subwoofer would blend in a more satisfying way with the sound of your main speakers. I own a pair of Dunlavy SC-IV's and I'm considering to add a REL subwoofer to the system. I can buy the Stentor III, but maybe the Studio III would sound better in combination with the Dunlavies. The folks at REL say that one Studio subwoofer is better than two Stentor's. I once red that the lower the main speakers go the better the subwoofer will blend with the sound. I also heard during a high end demonstration 8 years ago a pair of Wilson WATT 3/2 with a Pow Wow subwoofer (the size of a large coffee table) driven by Krell KAS amplifiers (+ Audio Research LS-2 linestage), and the sound was the most impressive I've ever heard.