e268, you've got a false assumption there...
Those Powerline speeds are maximum rates (i.e. "up to 200 Mbps"), not guaranteed rates...and it's a theoretical maximum (as in, that's the most they'll do, given optimum environment and circumstances). Neither maximum speed (200Mbps nor 85Mbps) would really be seen.
Myself, I'd go with the 200Mbps. Actually, that's what I've done--the Belkin Powerline AV Starter Kit
--and they work great. Powerline setup is generally quite simple, but the Belkin setup was dead simple (nothing to setup on the PC; just plug 'em in, and then press the buttons to reset the encryption).
Another nice feature of the Belkins is that you aren't forced to have the whole unit hanging from the wall plug. Included in the box is two backplates per adaptor:
- backplate to plug straight into the wall socket
- backplate to an extension cord that plugs into the wall
Returning to the topic at hand (speed), here's the blurb on the box about operating range ("Up to300m in wall powerlines") and speed ("Up to 200Mbps"):
NOTE: The standard transmission rate--200Mbps--is the ideal physical data rate. Actual data throughput and distance will be lower, depending on interference, network traffic, building materials, and other condictions.
Your 100Mbps router likely won't be limiting the speed of Powerline AV communication to a significant degree, if at all. In addition, 85Mbps wouldn't be seen from 85Mbps units. Combine the two, and the difference in speed should be higher than the 15Mbps apparent at a cursory glance.
I can't guarantee what speed you would get, nor can I say whether the speed difference is worth it to you. Just trying to get the parameters of the question off the maximum numbers since those aren't really seen.
Anyway, I've rambled on long enough. Hope that helps.