The state of your electrical wiring will effect speeds as well, how old is the house/wiring?
I use the SAME homplugs.
I get 62 Meg to one computer and about 28 to the other (upstairs). Modern wiring in the house.
The only difference is that the upstairs homeplug has to be on a 4 way strip with the computer, printer and monitor (which is know to cause issues).
Try to make sure the homeplug has its own socket and is not on a strip, especially one with surge protection.
Let us know if this solves your problem (even if it means a longer run round a room to get to another mains plug!).
I use 200mpbs homeplugs also.
I get 75mb direct wire from router and (after a lot of messing around) I get 62mb using homeplug. At first I was only get half that speed with the homeplugs until I relised that if you are using 4 way extention leads for several appliences, it effects your speed. Try plugging the homeplug into a socket of its own, so its getting full power from the socket. Do the same with both plugs and you should get better speeds, worked for me anyway.
In some buildings the upstairs and downstairs sockets are on different rings [but not all].
To do a quick test,plug a table lamp into a downstairs socket and another one into an upstairs socket and turn them on.
Then go to your fusebox and switch off the fuse switches that feed the 2 rings [if it has 2],if both lamps go out with 1 ring switched off then they are both on that ring.
If you have to turn off 2 fuse connection switches to get both lamps to go out then you have your homeplug devices on 2 rings which could cause problems.