Whatever is "best" theoretically, I suggest you do two things. First, some pricing research to see how both scenarios play out. Generally speaking, interconnects cost more per foot than comparable-quality speaker cables. So you might -- MIGHT -- be better off in terms of bang for the buck by going with the longer speaker cables.
Second, be careful not to lock yourself into something you can't easily change or experiment with down the road if you should want to. For example, if you could split the difference (2- 3-meter ICs and equivalent length speaker cables -- not sure this will work in your layout) you'll leave open more options down the road, since those lengths are plentiful in the used market. Once you get into 5M interconnects, you get pretty short on options.
Second, be careful not to lock yourself into something you can't easily change or experiment with down the road if you should want to. For example, if you could split the difference (2- 3-meter ICs and equivalent length speaker cables -- not sure this will work in your layout) you'll leave open more options down the road, since those lengths are plentiful in the used market. Once you get into 5M interconnects, you get pretty short on options.