If it's any help, I'm 5' 11 and 1/2" with a 32" leg. According to Giant's website, I was over the cut-off point between M and L. However, I can tell you that the L was...well...too LARGE and left me sprawling forward with my crotch (gross word) too close to the frame, so I bought the M instead, as it still fitted perfectly to my leg length (bloody long seatpost!).
In terms of forward reach, I have an 11cm stem on my bike (by the way, it's an OCR1, but pretty sure it's same frame geometry as the TCR you're contemplating), which when I first started to ride on left me feeling a bit cramped and thinking about buying something a bit longer to compensate for that bunched up feeling (the upshot of buying the smaller frame size).
However, turned flip-flop stem over instead for different handlebar position and now feel fit is just fine. A longer stem is so easy to get hold of, giving you plenty of opportunity for greater reach, whilst the supplied seatpost - at 350mm - gives plenty of room for manoeuvre to suit your leg length, providing they're not excessively long or short.
The benefit of the Giant compact frame is that these components make alot of difference within the framesize and can greatly reduce the chance of you ending up with the wrong-sized frame. Be aware of this - you can't start sawing out sections of a L frame to reduce it in size, but you can change stem, seatpost and cranklength without much hassle, i.e. the M may well still be your best bet.
If you can't get a TCR to test-ride / measure up on, can you get onto an OCR instead? If you can't do that either, have a look at the Giant webpages on Philosphy and Sizing at;
http://www.giant-bicycles.com/uk/050.000.000/050.045.500.asp
however, bear in mind what I've just told you about my experience of using this info, as well as what Boudreaux, Rudy etc have said about it being more than just height.
If you are serious about making this purchase, you really should be at the very least getting on the thing before committing the cash; would you buy a car without taking a test-ride? I do sympathize about the wait - Giant roadbikes seem to have been in really short supply since the Autumn - but it really would be alot less frustrating to do be TCR-less for a bit than it would being lumbered with something pretty expensive that just doesn't fit properly, and which makes your cycling experience [censored]. Where do you live in the country? I'm presuming you're in the UK (feet and inches, you see!).
Seriously, listen to what these people are saying on this site they've given me a hell of useful advice over the last five months. And if they've got a good rep, use your local bike shop's expertise as much as possible too; if you give your location, I'm sure someone on the forum could help with pointing you in the direction of a decent LBS.
There are plenty of people willing to help, my friend - make use of them!
Good luck and let us know how it goes.
MG
