So I just got my standard opened just now. It is a delight and I love it.
Verdict: it really isn't that loud. Louder than the S, yes. But no louder than my officemate's Microsoft Natural 4000. The sound has two parts : a very nice "thock" on the way down. On the way up (sometimes, but not all) there's a bit of a "clack" as the key reaches the end of the stroke. It's not loud at all, but might be more intrusive than the thock.
Here's my reasoning: First, you'll want Hasu's mod; save the money for that. Then if you love HHKB (like me) you'll probably end up with both eventually. If it's not for you, GH is an easy place to sell it.
Second, the dark grey/black keys are gorgeous. Esp w/ the red/blue Ctrl/Esc color pack. It just makes it for me. See pix:


Finally, most offices I've worked in are loud: people talk, type, phone calls, etc. My gentle typing on this thing is within the thresholds of office politesse I've experienced; doubtless others have experienced officepsaces with lower noise thresholds, which seems like a good problem to have. YMMV.
I'm going to try my luck with the standard first; yet look forward to the inevitable day when I also buy the Type-S...just for the joy of it. Let us know what you decide and how it works out
-R