I did a migration from Windows 7 to Windows 8, no clean install, This way i did not have to reinstall all SW I have on the PC. (Vista to Win 7 migration I did some years ago) I have an ATI HD4850 graphic card. ATI does not support this card any longer, hence ATI does not provide WIN 8 drivers. However, Windows 8 supports this graphic  card with own drivers.   The Motherboard Bios I updated years ago to Version 1.1.4 What surpised me is that my Miccrosoft Webcam, LifeCam VX-6000, is not Win8 compatible.  It still works under the Desktop mode of Win 8 e.g. in Spype. But using the Metro version of Skype the camera is not visable. So I bought a new one. VirtualCloneDrive I had to reinstall after upgrading to Win8.   Most things the Win8 compatibility check stated it is not compatible I deinstatlled bevor migrating to Windows 8.  But it was only a few items listed.
I see that the XPS 435 T is not recommended for Windows 8. I have the XPS 435 MT will it be able to run Windows 8? 
XPS 435 MT and Windows 8