Hy,
I faced the same problem with a very slow gc.com site depending on the daytime I used it. And I can confirm that the Telekom routing theory seems to be right.
Here's my observation:
My DSL provider was German Telekom until 4th of may 2015. The geocaching.com site was often very slow, sometimes unusable. I am located nearby Nuremburg in the south of Germany.
When I set my Smartphone to Wireless HotSpot mode and used the mobile data connection, gc.com was much faster.
Since 2 days my new DSL provider is M-net and the problem is gone
Summary:
Performance problems with Telekom DSL, no performance problems with mobile data like LTE or M-Net DSL. Does not sound like a service problem on geoacaching.com side. Sounds like an internal Telekom routing and bottleneck issue.
hope that helps, regards, f r e d