Monster advancement, Exp and CR

In the MM it states that the CR of an advanced creature stays the same but the experience points are increased so if you increase the HD by 50% the PCs get 150% of exp and so on...

However I am sure that I read somewhere that this had been modified sio that the CR of the beast goes up by one for each half that you increase the HD of the creature by so:

A Gargoyle has a CR of 4

A 6HD Gargoyle has a CR of 5

A 8HD Gargoyle has a CR of 6

A 10HD Gargoyle has a CR of 7

and so on...

Which is correct?

Thanks in advance

The latter, though it's not terribly accurate.

Neither of them work particularly well in my opinion...