Just like hot rod car stuff, speed is directly proportional to investment so you can go as fast as your wallet allows! Of course there's always the issue of knowing where to spend the money to get the most out of your investment. In sound systems, the weakest link is almost always the speaker transducer, so buying quality motors is undoubtedly the single most important determiner of sound quality.

All that to say that I think you've put together the right stuff to make an outstanding loudspeaker system! I wish I could be there to see and hear it, so please post photos when time allows.