Nap,i will be running at least 4 to 5m for the front L/R,abit shoter for the center and it will be shorter if ever i decide to mount my TV on the wall,thats the decision that i have to make ,coz my TV rack is about 3m long.As for the i/c`s what i have notice and read in here,most of the Brytons fans use the xlr rather then the rca.Is there any benefits in doing so?I wonder why the Bryston xlr used the headphone connectors. 
Make the speaker cable 10 gauge or better and it should serve you well. If you can order the Van Damme that Bryston sells/uses, go for it.
As for interconnects, XLR will give you better S/N ratio, you can check Bryston's specs, they have separate numbers for balanced / unbalanced and the balanced numbers are better. For the 4B you'll have a 3 dB difference which probably comes from the fact that in balanced mode the first amplification stage is bypassed (thus it won't contribute to noise anymore).
Nap.
P.S. These differences might not be audible. E.g. my 4B is dead quiet no matter what I select (balanced or unbalanced). But just for peace of mind you can go for the setup that would give the best measured performance.
