I have started looking at CC bikes recently and propably spending roughly 1300-1800€ and expecting to get good bike and value for my money.

This Ridley X-Ride 1203C1 Ultegra 2013 looks pretty ok, but I'm currently wondering a bit which would be the best frame alternative?
I'm 172 cm tall and inseam lenght was something like 78cm.
In this case, looking at sizing table/recommendation for Ridley CC, which is more relevant, rider hight or inseam lenght?

Frame Size Rider Height (cm) Inside Leg (cm)
41cm 155 67 - 78
48cm 170 78 - 81
50cm 173 81 - 85

Would you recommend going for 48cm or towards 50cm frame?
I would imagine that the difference is not too big, but then again buying blindly from net and possibly spending even ~2000€ I would prefer having bike as optimal as possible.
My current MTB from 2003 (Kona Kikapu) is of size 18" and it feels just slightly oversized for me.

I will most likely start riding regularly from home to work (~15km one way) so if weather is not totally awful or not too sophisticated meetings expected early morning I'll be propably "collecting" ~100-150kms a week and as I live in Finland there will be some winter riding included = spiketyres must fit in including mudcovers etc.

I hope I can find some dealers which would have somewhat correctly sized frames available for me to test, but quite often the demo bikes are for cyclists of size 176-190cm or something similar, it's not fun testing oversized bike and then only hoping the smaller frame suits well.

Drop me some comments if you would clearly recommend certain sizes.
I'm into CC with disc breaks, and preferably a bit better set of derailleurs and so on (ultegra or 105 minimum + Avid BB7) and so on, haven't had SRAM ever, but it's not totally out of question.
I'm not so worried about bike brand, but rather more interested that the geometry suits well for shorter driver.