An EFI-mode boot is unlikely to affect Ubuntu's performance once booted. The system might boot a little more quickly in EFI mode, but that's all the performance improvement you're likely to see.
That said, if you want to do an EFI-mode installation, the key is to ensure that your motherboard boots the CD/DVD/flash drive in EFI mode rather than in BIOS mode. How to do this depends on the firmware. Some offer clear and obvious options in their boot screens (usually selected by pressing F8, F10, F12, or some other key at boot time), but others provide few or no options to control the boot mode, which means you can only control this detail by preparing a boot medium that lacks the boot loader for the mode you don't want to use.
As a side note for Geezanansa (and anybody else who may be interested), rEFInd 0.4.6 and later supports booting both EFI-mode and BIOS-mode OSes if your firmware provides appropriate support. The BIOS-mode boot options are disabled by default on UEFI-based PCs (but enabled on Macs), so to use this feature you must edit the scanfor line in refind.conf to scan for BIOS-mode boot options. This feature is still a little klunky, but I've used it to switch between EFI-mode and BIOS-mode boots of Linux. It could be a quick fix if you accidentally install Windows in EFI mode and Linux in BIOS mode -- install rEFInd from Windows and then when you boot, you should see a boot menu giving you both Windows and a generic BIOS-mode boot options. The first will start Windows and the second will launch GRUB 2, which in turn will launch Linux.
An EFI-mode boot is unlikely to affect Ubuntu's performance once booted. The system might boot a little more quickly in EFI mode, but that's all the performance improvement you're likely to see.
That said, if you want to do an EFI-mode installation, the key is to ensure that your motherboard boots the CD/DVD/flash drive in EFI mode rather than in BIOS mode. How to do this depends on the firmware. Some offer clear and obvious options in their boot screens (usually selected by pressing F8, F10, F12, or some other key at boot time), but others provide few or no options to control the boot mode, which means you can only control this detail by preparing a boot medium that lacks the boot loader for the mode you don't want to use.
As a side note for Geezanansa (and anybody else who may be interested), rEFInd 0.4.6 and later supports booting both EFI-mode and BIOS-mode OSes if your firmware provides appropriate support. The BIOS-mode boot options are disabled by default on UEFI-based PCs (but enabled on Macs), so to use this feature you must edit the
scanforline inrefind.confto scan for BIOS-mode boot options. This feature is still a little klunky, but I've used it to switch between EFI-mode and BIOS-mode boots of Linux. It could be a quick fix if you accidentally install Windows in EFI mode and Linux in BIOS mode -- install rEFInd from Windows and then when you boot, you should see a boot menu giving you both Windows and a generic BIOS-mode boot options. The first will start Windows and the second will launch GRUB 2, which in turn will launch Linux.On your system, switching to UEFI mode will not bring improvement.
However, if you still want UEFI, you will have to use Ubuntu
64bit, and follow https://help.ubuntu.com/community/UEFI