Well a cable is always way better especially if it's a fibre cable. High gain antenna remain susceptible to throughput loss and since the rf spectrum used by wifi is unregulated it competes with other wifi device making connection over significant distances very poor.
However, since you still want ot use wireless, I would suggest you try point to point professional radio which are specifically built for this purpose. In cisco land U might be looking at an Aironet 1500 but that wld be too much for such a short distance and unnecessarily more expensive. Look up for cheaper options.
Just something you can check out: http://www.focus.com/briefs/mobile-wireless/10-tips-increase-wireless-range/