I don't know as far as Nvidia, however make sure you understand that CLU isn't paste. It's literally gallium which is liquid at room temperature and you basically are soldering your heatsink to the chip. It molecularly bonds to the metals and can never really be completely "cleaned off"
That being said, I have used CLU on 2 AMD R9 290 cards and a 2011 i7 with great results.
There aren't HUGE gains to be found on a GPU since the die is pretty big for the TDP but in my opinion I'll take whatever I can get.
I did a thread showing pictures of the process for anyone wanting to see what CLU was like before going that route