OK guys, sorry but here's a rather long 'update'.
Right, I had a minion measure me and used the calculator @
michaelcycle gave me and it threw out some results for me. My problem now is that I don't really know what I'm doing.
I've been reading up on bike fitting and am still unsure of what parts of the geometry are the most important and what sort of margin for error there is, it seems either the seat tube c-c or top tube on any bike is 'wrong' according to the calculator. On top of this I've had a change of budget due to my family coming around to the idea of me cycling around places.
As such I was looking at a Cannondale caad8 105 5 2014 (I actually fell in love with the blue version @
vickster 
(no sarcasm)) as my LBS can get this in and I will get a 10% discount as a club member; I'll also get it fitted and two years servicing for free which I think is a good deal. I should also be able to test ride one also. I'm just terrified of spending just shy of 1K on a bike only to discover it's not the best fit. My 'hybrid' is basically a hardtail with its current gearing and I'm not spending money to stick higher gears on, I'm just going to buy a cheap winter / rough bike; that's right I'm now getting two bikes

.
I just thought I'd ask for some more advice before I do anything. How accurate is the whole bike sizing thing? Is the Cannondale a sensible choice? Should I *TRY* to get the second-hand winter bike first so I get a feel for what works in terms of size? It's a shame there are no red triban 3's going as one of them would have done the job. I feel a bit overwhelmed by all the changes of plan, which is utterly my fault

.
Thanks in advance.