I agree that almost any room size will work with the 2s. The 3s will benefit from a larger room, but I have heard them work successfully in a few smaller rooms also. It is important to remember that with Vandersteen's 1st-order floor-standing speakers (Models 1, 2, 3, Quatro and 5) you need to sit at least 7 feet away from the speaker in order to achieve proper blending of the drivers regardless of the overall room size.
The more important difference between the two models is that the 3 is more demanding and sensitive to the electronics you choose, especially the power amplifier. Where a good 50-60 watt amplifier can work well with the 2s, the 3s prefer larger higher-quality amplifiers typically in the 100 watt/ch range or higher. The 3's will also be more revealing of the quality of the electronics in front of them.
Both models can also achieve even better sound quality (more like Quatros and Model 5s) and become much easier to drive when partnered with Vandersteen's "audiophile" 300 watt active subwoofer known as the 2Wq.
Good luck.
