I have a pair of Bredli together, and my enclosure is 1200x600x600. They are both three years old (well, the female is, the male will be on the 30th of this month!), they have a hollow log each, separate basking platforms above the heat source and separate basking sites below the heat source. They have been together now for two years, and 'seem' to get along well. There have been no outward signs of aggression, even in the early stages (were monitored very closely for this) and they are fed separately. Female in a tub, male stays in the enclosure. After an hour or so, when rats have been well and truly consumed, all stretches and yawns done, female goes back in with the male, and I monitor their behaviour again for 20-30minutes. They are fed medium rats fortnightly.
I also have a pair of Murray Darlings together, their enclosure is 2400 x 600 x 600. Same amount of hides, basking sites etc as the Bredli and my female is 7 years old, my male is 9 years old. I take the male out for feeds (he prefers this!), and follow the above routine as the Bredli. They are on large adult rats (probably should be on small rabbits, but...!), fed fortnightly.
All this being said, if you keep the same species of the same age together, monitor them as closely as possible, feed separately, you "shouldn't" have too many problems.
Best,
Carolyn