I did some more tests last night, this time just running Workstation 11.0 and the Windows 7 guest that I newly created in Workstation 9.0.3.
If all I do is power it on, and not upgrade the virtual hardware (and VMware tools) then the performance seems to be the same as in Workstation 9.0. If, however, I upgrade the virtual hardware (and VMware tools) the performance degradation kicks in.
Running in WS11
WS9 Hardware:
Processor: 6.9
RAM: 5.5
Graphics: 6.0
Gaming Graphics: 6.0
Primary hard disk: 6.6*
WS10 Hardware:
Processor: 6.8 (-0.1)
RAM: 5.5
Graphics: 4.3 (-1.7)
Gaming Graphics: 4.7 (-1.3)
Primary hard disk: 5.9 (-0.7)
WS11 Hardware (256Mb video RAM)
Processor: 6.8
RAM: 5.5
Graphics: 4.1 (-0.2)
Gaming Graphics: 4.7
Primary hard disk: 5.9
* I often wondered how WS9 would report better primary disk access than the host; I assumed some kind of internal I/O caching or similar. Whatever the case, that benefit seemed to be lost in WS10 and stayed that way in WS11.
Most of the reported performance hit is when changing to WS10 hardware (notably the primary hard disk too), but the graphics component of the WEI takes a further hit on "upgrading" to WS11 hardware.
My excitement and anticipation of WS11 has been somewhat dulled by this result since I mainly run Windows 7 guests, although eventually I'll want to run Windows 10 (and couple Linux) guests.
I'll do some testing with Win8/10 and add my findings later.