i had the same problem at my fathers house (telekom too) so i though it would be btct having some bandwith or cpu issues.
new isp (ok only until today...like 10hrs) no problems, and i have never seen this speed before (my connection speed didnt change that much; probably better route to the btct server though)
i will monitor it. but if theymos hasnt changed anything recently and it stays like that the next days i am convinced they cripple it: not sure why too
interesting; 502 i got very rarely. half loading pages where common (at least for the last 3three month i got them daily)