Vacheron Constantin

Hello Guys

I am trying do some research before buying my first vacheron, I basically narrowed it down to two models VCO 42042 (37mm) & 49140(40mm).

I always thought the 37mm looked too small( although never got to try one in my wrist) but I am surprised (looking at the pictures of the two side by side posted recently by a member here)the 42042 does not look that small compared to the 49140 .I have a 6.8 - 7 inch wrist size and 38mm watches look perfect on my wrist but i think a chronograph like 49140 if its 41mm(with crown) might look a bit big.

I am searching for a good overseas 42042 chronometre to buy but very confused as there are different sizes & calibres. 

I have checked ebay and chrono24 for 42042 ,Could anyone advise best place to buy authentic vacheron chronometre 42042 from and how to check authencity , & which is the best calibre VC in the 42042.

Sorry for all these questions any feedback would be appreciated,just a bit worried as this is my first time buying pre owned watches from the internet, and was reading some where that  there quite a few replicas of overseas 42042 sold throughout the web.