upgrade/change nvidia driver versions with envyng-gtk 2015

Hi Folks -

Am running 14.04 LTS on AMD 64 with nvidia card, most often a 9100 integral but sometimes a higher end nvidia card, and nvidia indicates I use the 340 driver for both cards but I have been using 304, maintained by xorg/edgers PPA for some time now without apparent issue.

But I would like to change drivers to the 340 nvidia says I should be using for both cards as the 9100 integral has been overheating lately and it is not a physical dust-blockage issue.

So my question is can I use the somewhat dated envyng-gtk to safely purge the current xorg nvidia 304 and install 340? And if envyng-gtk is not a practical option, what steps should I follow. And should I use the NVIDIA-Linux-x86_64-340.76.run file and instruction from the nvidia site instead of xorg/edgers? I'm dual-booting and do 3D CAD work in win7 but also in ubuntu14. Have been all over the web and so much conflicting information regarding this issue.

Certianly I have backups (clonezilla by disk and by OS) but I really don't want to go thru all that if it can be avoided.

Thank you, and thank you all for your open-source efforts.

gt