Hey, Boys and Girls!

Long-time reader...first time poster here!

I took up road cycling 8 months ago, and I'm loving it. Currently riding a $300 Bikesdirect.com bike- and while I have absolutely no complaints with this bike (I'm really impressed and amazed at what I got for the price) I've always wanted a Klein Quantum (pre 2002, of course)- so I've been looking on Ebay, etc. but I am unsure as to what size I need- and geometry info for these bikes is not so plentiful, and I've read some conflicting info- so I was wondering if anyone on here is familiar enough to give me some guidance?

My current bike is a 54cm and fits me like a glove. Wouldn't want to go any bigger- could go a size smaller and still be comfy, I think.

I'm 5'10". 31" cycling inseam.

Geo of current bike:
Seat tube center to top=54cm
Effective top-tube length=56.5 (semi compact frame)
Head tube length=16.1
Reach=39cm

I'm thinking a 53 or 54cm Klein'd probably do me.....but for some reason, I see very few in that size- most seem to be 56cm or bigger. I've seem some specs that make me think I could go 55 or 56....but naturally, I'd like to know for sure before buying one.

Anyone?