Blazers -- size up or down?

[cjl]

So I am probably a 41R in most off the rack suits, which means I'm forever deciding between 40R and 42R. Trying to purchase my first blazer and ended up with this one in both sizes for $75:


http://www.cladmen.com/on-sale/suits-and-jackets/wool-two-button-blazer.html


Should I size up and take it in, or size down and maybe be more contemporary in appearance than I feel as a 33 year old diplomat with two young girls?

[OnlyShawn]

Size inversely proportional to your balls.

[jason_carreira]

You just have to try things on and see what fits. You can't get a jacket's shoulders brought in or out.

[nicholascrawford]

Every line of clothing will run bigger or smaller. You can get a feel from reading reviews, but you'll never know till you try it. I'd order both if you can and return the other.