You have a Graphics card fitted at the moment. To replace that card with another card may not be "Out of the Box" compatibility. What settings did you use for the Sapphire HD6450? If all you used was GraphicsEnabler=Yes and you are running 10.8.4+ then it should be a simple changeover.
Adrian B
i'm using this sapphire hd6450 512mb with GE yes (if no, no fullhd output), with enoch (chameleon base) injunction of framebuffer and ports, with KEXT REPLACE.. expecialy, if i'd want to boot the osx installer i have to delete ATI6000controller.kext and put ge=No, or it will not boot in the installation..
in the normal usage, i have to put setting that you saw up on here, and sure, i have to rewrite the kext with the old ATI6000controller
all ok till 10.8.5 witch it freezes my pc.. i changed ALL graph text with the 10.8.4 and now i'm on 10.8.5.. but i spent hours to find that bug, and sure, 100GB of my samsung 830 SSD
so, i prefere to have a full out of the box card witch doesen't need any kext replace, even with maverick, since i don't have a fast pc (i'm on zotac ion itx p-e with cpu @1.88ghz and 4gb ddr3 @ 1250mhz) and i'd want to install maverick witch has some good features to decrease the load of the cpu.. and sure.. the cuda cores could be usefull for me, better hardware acceleration than HD6450
so, for me it could be a good upgrade if i buy the gt630 with kepler arch.. but i have to know if it works out of the box.. i don't want to replace kext everytime i have to upgrade the osx
btw, my mobo has the ion chipset with the 9400m graph card.. it's the same chipset as the mac mini 2009.. the cpu is a classical core2duo, it means i need only one fakesmc and 1 kext injection for the SSD using by a minipci-e sata3 card
so, the only thing witch create issues on my desktop is the graph card.. and i don't want to come back to the 9400m, it uses the ram as vram, and it's slower than hd6450
thanks for fast answer!!