The 64 bit client was not running NVIDIA graphics chip, instead using the built in Intel chip.
By right-clicking on eso64.exe and choosing from the context menu "Run With Graphics Processor --> High Performance NVIDIA Processor" I now get the same FPS in 64bit as in 32bit, same as before TG patch.
I have now used the NVIDIA control panel to specify that the NVIDIA processor should always be used when running eso64.exe
I hope this fix works for others as well.
EDIT: If you do not have that choice in the context menu, I have posted another solution in this thread:
forums.elderscrollsonline.com/en/discussion/252829/64bit-fps-issue-solved#3
Cheers!
Edited by ContraTempo on March 12, 2016 10:44PM ContraTempo
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