So far, I've ridden the 16 inch MERIDA and the 18 inch MERIDA bikes.

I can say that the 16 inch seemed cramped, it was almost as if my hands wanted to grip the handle-bars a little 'beyond' where they were.

The 18 inch MERIDA seemed 'roomy'.

The sales-staff said that I would be possible to shorten the stem-extension on the 18 inch so that the handle-bars were a little bit closer in. This would -so they say-shorten the bike a bit.

Is there some 'sticky' post somewhere that describes (in detail) how to fit the bike and what to look for?

I've read a heap of advice elsewhere on the net and even watched some youtube videos but they all assume that people want a mountain-bike for hitting the trails and rock-gardens.

I'm still wondering if a little more length also means the top-tube is longer and therefor more roomy.

Cheers