I am looking at buying an 04/05 Marin Rock Springs (I know its an old model but its a bargain) from Winstanleys

Obviously with it being such an old model there is an issue with getting a test ride on different frame sizes as availability is limited.  Also I know the important thing is to try the bike as well, however as a rough guide could anyone tell me what sort of frame size I should be looking at (it would be either the Small or Medium)  I am 169 cms (which I think is 5'6 and a half) of relatively normal proportions

Thanks for any advice

Clicky may be of use.