I will give a more precise answer.
Remember that reference cooling may refer to traditional style and non-traditional style. Traditional style means 'front centrifugal intake fan with rear exhaust alone'. Examples are reference HD6970/GTX570. Non-traditional style means everything not traditional. Examples are reference HD6990/GTX560Ti.
So, I suggest getting a card(s) that is not only reference but also of the traditional style. Silverstone actually addressed this issue of using non traditional style cooling cards. There are 2 areas of concern for a non traditional style cooling cards:-
(1) hot exhaust coming out from the front of the card which will go against the uprising fresh ambient air. This will result in hot air recirculation.
(2) heatpipes pointing downward and the working fluid within will have to work against gravity pull. This will result in a reduction of the cooling capacity.
So, Silverstone recommends using cards of reference traditional style.
See my post #4 in this thread for more info:-
http://www.overclock.net/t/1176895/corsair-h60-fit-in-a-raven
Note: Many users report 'good' cooling despite using non traditional style cards. So, this is not an issue of life-or-death but it is just not making maximum optimal cooling of the cards and the case.