I did some further research.
The original number quoted from Wikipedia must be out-of-date, because other sources claim a negligible hit in performance with FileVault2, even when being applied to a mechanical hard drive. I assume the Wikipedia article was referencing the performance of FileVault2 on a machine that doesn't use a more recent Intel processor. The reason I assume that is because apparently FileVault2 now takes advantage of hardware acceleration offered by Intel processors for the software encryption process. This is for Macs that use an Intel processor from 2010 and later; as is discussed in these three links:
http://apple.stackexchange.com/questions/105320/does-filevault-encryption-slow-r ead-write-access-on-an-ssd
FileVault2 Performance
http://osxdaily.com/2011/08/10/filevault-2-benchmarks-disk-encryption-faster-mac -os-x-lion/
There's still a downside to using FileVault2 over hard drive facilitated encryption; though, which is a vulnerability to hackers retrieving the encryption password from the memory of a Mac that is still powered on. This info is from an article published in 2012, so maybe Apple has patched that vulnerability by now? I didn't see any mention of that, though.
https://www.cnet.com/news/filevault-2-easily-decrypted-warns-passware/
In the mean time, a way to account for that vulnerability would be to always power down the Mac when not near it instead of allowing sleep mode.
https://www.engadget.com/2012/02/03/apple-filevault-2-encryption-cracked-but-don t-panic/
So although there's probably negligible difference in performance between hardware encryption and FileVault2, there still seems to be better security with the hard drive's hardware-based encryption.
All of this info ultimately leads back to the original question. How does one go about accessing the UEFI/EFI on a Mac and enable the hardware encryption of the hard drive?