Once a week I usually have to reboot my 2710 in an attempt to sync with the exchange at a higher speed.

I have to regularly monitor the sync speed of the 2710 as, one day I can resync at 448/6960, only to find that a a few days later this may have dropped to 448/5696 eventhough the router has not been rebooted.

Is it normal for a sync speed with the exchange to drop without the router being rebooted ?

Should be, most routers will have SRA (seamless rate adaptation), so if the SNR of the connection drops or it detects enough errors, the router and exchange hardware will agree to drop the speed a bit.
With my line for instance, if it rains, my sync speed goes about 1mbit lower

Thanks for the post Voodle.

That makes sense now. I'm glad to hear my router doesn't have a problem.