MEI Firmware always did not affects system performance. It was provide more security and protecting against backdoor or root admin attack via USB ports.
By the way if you want to flash older version of MEI Firmware. You can use this command via FWUpdlcl64 Tools.
C:\> FWUpdlcl64 -F "XXX.BIN" -ALLOWSV then hit enter.
Note :: "XXX.BIN" = your old MEI Firmware binary file.
W11CANARY 26090.1 Core i9 7980XE 02007006 MCE ME 11.12.95.2499 R6E OFFICIAL BIOS 3801 SAMSUNG OG9 FW 1019.0 SSD 970 EVO PLUS 1 TB x 3 NVIDIA RTX 4090 GAME READY 551.86 64GB GSKILL DDR4 3200MHz JBL 9.1 Sound Bar DTS-X