Unless it's constantly slow leave it alone, the line speed will vary during the training period.
Also it will just be slower sometimes due to contention, I find the speed drop in busy periods much more noticable with FTTC than I ever did with ADSL, mainly I think because you get used to almost instant access to everything and then even a slight delay seems like a big slowdown.
It won't do much harm to reboot once, but if you do it several times the exchange will think your line is unstable and drop the speed further to try and stabilise it.
Cheers,
John
