Hi, may be a stupid question that I already know the answer to but what exactly is the best connection possible betweeon two original xboxes for system link? My answer would be a CAT6 crossover cable, but is there anything better?

Crossover cable or straight running through a hub or switch. Depends on the length of the cable. In a house you won't have problems with a cable. I haven't tried Cat6, Cat5 works just fine and is probably cheaper.