To fix the problem on Linux, use iptables to reject the throttled cache and go direct to Google servers:
sudo iptables -A INPUT -s 188.8.131.52/24 -j REJECT
sudo iptables -A INPUT -s 184.108.40.206/16 -j REJECT
While it's possible the throttling happens because caches are bottlenecked or overloaded somewhere in the ISPs' network, complaints to forums have elicited 'We have no problems' responses."
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