Firstly why are you using an ad-hoc network when you have one server and
several clients (which do not seem to need to talk to each other).
Secondly, what exactly do you mean by link quality. There is no simple
static number which would equate to an ethernet speed, and some of the
protocols confuse data rate measurements by forcing management packets
to run at the slowest possible speed. You also have to take contention
into consideration, and if you use ad-hoc that will be worse that if you
use an AP with attached clients - especially if you poll the clients from
the server rather than having arbitrary packets being sent from the clients
and colliding.
David