Colin, I'm seeing very similar problems as you.
I've got some Solwise 500AV homeplugs.
I get a nice 100Mbit/s+ transfer rate between downstairs and upstairs.
I get 74Mbit/s+ on the Internet downstairs.
But upstairs, I'm limited to around 40Mbit/s on the Internet.
Except that in one case, running 15 ssl connections concurrently, I can get the full 74Mbit/s.
I'm wondering if the homeplugs have speed issues with IP fragmentation, because if I lower my router's MTU to 1430 from 1492, I get odd speedtest results, some up to 60-ish Mbit/sec.
Additionally, I'm wondering if not using 1500 byte frames are affecting the homeplugs speed-wise.
-- gyre --
Edited by gyre (Thu 07-Aug-14 13:18:49)