Under R340, both Fermi and Kepler will run in WDDM 1.3 mode, which makes win10 happy.
Under R352, Kepler will run in WDDM 2.0 mode but Fermi will run in WDDM 1.3 mode, which makes win10 unhappy.
(presumably this will be fixed at some future date, in some future GPU driver version)
R340 = drivers whose versions are in the 340.xx - 341.xx range
R352 = drivers whose versions are in the 352.xx - 353.xx range
Kepler = GeForce 6xx, 7xx mostly (there are exceptions).
Fermi = GeForce 4xx, 5xx (again, there may be exceptions.)
If you think you have a config like this, please try an R340 driver that is listed as compatible with both or all of the NVIDIA GPUs in your machine.
Use the driver wizard at www.nvidia.com … Drivers
Yes, to use an R340 driver you have to select one from Win8.1 in the wizard, not Win10