When it comes to period correct or not I exclude power supplies, cooling, optical drives and to some degree storage.
Non of these affect the performance except perhaps storage but for for example using a small flash DOM with a bog standard ISA controller does not bring more performance than using a noisy period correct SCSI drive with a cashing SCSI controller.
Running Winmark my all ISA DX50 build (in progress, DX2/66 atm) with a 256MB Transcend DOM gets pretty much the same disk score as the best score PC Magazine got when they tested DX2/66 systems, the PC Mag system used a fancy caching controller. As long as the performance dosn't get totally unrealistic not having to listen to a noisy SCSI drive makes it worth beeing a bit less strict and I still consider the build "period correct".
I also substitute other stuff.
1991 there was an ISA video accelerator card called the Opta Mona Lisa. This card had a Tseng ET4000AX with 512kB to 1 MB DRAM for VGA compatibility and a Ti 34020 accelerator chip with 2MB to 4MB VRAM for speedy performance in high and true colour modes in Windows. I do not own such a card but the ISA Tseng ET4000w32 has the same DOS performance as the Mona Lisas ET4000AX and at least decent Windows performance so it will have to be close enough.
If I would have been really anal I would have used my Orchid Fahrenheit 1280 with its lousy DOS performance or a Tseng ET4000AX with its lacklustre Windows performance. I would also have used an ISA caching controller with a nosiy but speedy hdd and probably not used the system much because of the racket it would have made.
New PC: i9 12900K @5GHz all cores @1.2v. MSI PRO Z690-A. 32GB DDR4 3600 CL14. 3070Ti.
Old PC: Dual Xeon X5690@4.6GHz, EVGA SR-2, 48GB DDR3R@2000MHz, Intel X25-M. GTX 980ti.
Older PC: K6-3+ 400@600MHz, PC-Chips M577, 256MB SDRAM, AWE64, Voodoo Banshee.