Thanks for your reply ben81 - in theory I agree with everything you’ve said.
But… in practice I’ve found our UEFI gaming laptop, an Asus G750JS, only seems to run smoothly with either Win8.1 (that it came pre-installed with), or Win10. Win7 will run, but only with CSM/Legacy on (Secure Boot off) in the PC’s settings. However Win7 isn’t worth running on this machine, as it will often go to a blue screen to “dump” before rebooting.
I’ve also found instability to plague WindowsOS/Linux dual-boots in either the CSM/Legacy or UEFI computer setting, and sometimes also in Linux-only single- or dual-boot setups. Even when I install with a Legacy computer setting, I always have to choose the UEFI option at USB-pendrive installation stage. A “Signature Key Violation” prevents me from installing the non-UEFI option from the USB-pendrive, so I have to always use the UEFI option on the USB-pendrive, for both Legacy or UEFI computer settings. Following a crash (failure to reboot), I will often then go into the laptop’s Boot settings and sometimes find that the Device Boot List has mysteriously cleared itself with no device at all to boot from !
I contrast the above experience with our 3 other laptops - all BIOS-only machines, manufactured from 6 to 10 years ago. On these machines, multi-boot & single-boot setups run extremely smoothly and there appear to be no stability issues - they are reliably rock steady. My favourite is our 10 year old Dell Latitude D630, that runs a Manjaro/Linux Lite/Win7 triple boot. I bought the Dell 2 years ago, from Amazon, for only £70: compare this with the £1200 paid out for the above Asus, that has been nothing but troublesome…