Slower wireless connection by one machine on g does not prevent faster connection by another on n.
I think the two cases of a slow machine slowing down another are: where the sloe machine is (very old) b,
or the fast machine is using linked channels on n (for 300Mbps) and the slow machine is not.
Moved (with trepidation) to BT Infinity 2 for upload speed. Happy BE user for several years.