Radeon HD video downgrade for patched-Mojave compatibility
Regarding the CTO 27" 2010 iMac with 2.93 GHz i7 processor, I attempted booting a machine of this model with a patched version of macOS 10.14 Mojave and succeeded, but true to warnings on the patch publisher's web page (dosdude1.com) video and other performance proved to be woefully inadequate. Apparently, neither that iMac's stock video card (ATI Radeon HD 5750) nor those of other 2010 iMacs (Radeon HD 5xxx series) can presently be made to work at all well with patched Mojave on unsupported Macs.
Reportedly, the 2011 iMacs with Radeon HD 6xxx series video cards also have this problem. However, the 2009s with Radeon HD 4xxx series video cards do not: They can run patched Mojave relatively problem-free.
Theoretically, a video card replacement might resolve this for me. The publisher says this himself in his instructional video for installing the patch (doing which to be clear he does not presently recommend for this model.)
In researching the practicalities of this, I have read that in general Nvidia MXM video cards can be considered for this upgrade. However, driver maintenance may be entailed, external power supply may be necessary (depending on card choice), and because these cards lack EFI a booting Mac's screen will remain dark until the login window presents.
Preferring friendlier options, I have researched further and learned that a 2009 or 2010 iMac's video card may be upgradable with a 2011's card. This makes me wonder: Can I do something like that but oppositely; that is, can I swap in the video card from a 2009 iMac for the card on my 2010 iMac?
Doing so would of course represent a downgrade in some degree. On the other hand, it could possibly have the special benefit of rendering my particular iMac patched-Mojave compatible.
Accordingly, I seek guidance. Has anyone thus downgraded their 2010 (or 2011) iMac’s video card or else confirmed the impossibility of so downgrading it?
Is dit een goede vraag?