Tone Publications has a review of twin Gotham G213s and it's hard to imagine doing better. The issue starts on page 130 of the downloadable ToneAudio Issue 26.
Also, I agree with what you're doing. I think picking the best subs you can afford is an excellent way to begin a system, because the subs determine the system's ultimate bass extension and dynamics and the maximum capability to energize and pressurize the listening area. The better the subs, the faster and deeper they are, and the more they determine the range of speakers that make the best match for the space and the capabilities of the subs.