Planning to change my router

[#1]

To improve the wireless coverage my house I plan to change my Netgear 11g/b router to a Belkin 11b/g/n. The last time I tried this I suffered a drop in speed that took days if not a couple of weeks to resolve. I am guesing that the BT exchange 'saw' the interruptions and resyncs and decided  the line was bad and reduced  the speed to compensate ? Is there any way that I can avoid this slow down happening again? I have already coded the belkin router with my Plusnet sign on details and the other line parameters (PPOA) etc. so the disconnection will only be for a few minutes.
Thanks
Mike   

[#2]

I'd do the switch overnight if possible as I think a long disconnection is less likely to be seen as a fault.
Turn the old one off in the evening and disconnect.
Turn the new one on next morning, verify the settings AGAIN (just to be sure) then connect to the filter and let it sync.

[#3]

Thanks for reply - finally got around to making change but Belkin stubbornly refused to sync at above 1250 and didn't improve wirelss range within house so changed back to netgear that immediately syncd at over 2000 - will  have to use higher speed home plugs to solve my problem.
thanks
Mike