Model M has particularly bad 2KRO blocking, so if you try to hit many combinations of three keys at the same time, the last doesn't register. Love those boards, but they are not a good choice for gaming.
Ideally you want an NKRO board, but they are rare if you want period-correct. Options:
1) Capacitive switches
- IBM Model F boards. Expensive. Rare. Non-standard (i.e. pre Enhanced Keyboard) layouts. VERY noisy.
- Foam & foil boards. Most vintage BTC boards use this. Two problems: 1) at best rather squishy and unresponsive. 2) after 25 years, they are far from best and require new foam and foil pads, adding to cost and effort.
2) Regular switches with diodes
- Cherry or Alps based boards with additional diodes to prevent ghosting. Great solution, lots of choice in switches (and so noise/tactile feedback), only problem is definitively figuring out if a given board has the diodes or not. Even within a specific model range (eg. Cherry G80-1000) their presence/absence is almost random.