Wow, Tony - that is one healthy-looking zygo! I have a B.G. White that is also very tall, has 3 pseudobulbs and one new growth, and is in a 5" plastic pot. Yours looks much better - if nothing else, it says a lot about the nursery that grew it (and I have no idea what that nursery is, nor am I asking for a name - that's for Bruce's benefit). Anyway, I think this is a tough decision. I'm not sure if all B.G. Whites bloom around the same time, but mine bloomed around Christmas, and the new growth started about a month ago. Your new growths look quite a bit bigger, which generally means that they have put down some pretty good-sized young roots already, which would be inevitably damaged at least a little in repotting. On the other hand, it DOES look like it's ready to split the pot open, so it's possible that the roots are so packed in, they're suffocating anyway.
Okay - so can I do anything besides make this decision harder? I actually come down on the side of not repotting it - 1)because it looks so healthy; 2) because the roots above the medium are live and healthy; 3) because of the potential new growth damage; and 4) because I've read that zygos actually like to have their rhizomes right at or above the medium, the way yours looks. Of course, if the medium is decomposing, then you DO have to repot it, but I can't tell from the photos, and it's unlikely the plant would look so healthy if it was.
If you keep it in its current pot, be sure to mist the roots above the medium pretty regularly, and you may have to water it more often because there are more roots than medium and the plant can't retain water as long with less medium.
BUT....now it comes to me - a good compromise might be to pot it up - that is, remove the entire plant, medium and all, disturbing as little of it as possible, and place the entire thing wholesale into a bigger pot and surround the spaces with fresh medium. If you can find a 7" pot, that would be good - if not, opt for a 6" - not an 8" - smaller is almost always better. And make sure you have it stabilized so it won't tip over since it's so top-heavy.
How's that for quick and easy answers?