it seems you have gone the cheaper way.
4,5 k needs more gpu ram than you have currently.
There is numerous post around here in the forum that you have probably missed.
—
Margus
https://iconstudios.eu
DaVinci 8.2.1 OSX 10.7.3
MacPro 5.1 2×2,93 24GB
GTX 470 / Quadro 4000
Multibridge 2 Pro