As everyone has already said, go for 3Dfx cards if possible, you will get better performance out of the Voodoo3 on a system such as this as opposed to even something like a GF2 or GF4 MX. It all boils down to CPU overhead, even a K6-3+ at 600MHz is usually slower than a Pentium 2 400.
When it comes to 3D FPU-intensive games, the K6-2 400 is hardly any faster than an MMX 233. That 100MHz overclock won't really do you much good.
As for the games you mentioned wanting to play:
Half-Life is borderline unplayable for me on such a CPU. I've tried it a couple of times on my K6-3+ 550MHz and it really struggles once more than 2 enemies get on screen or you go outside. I'm talking 12-15FPS sort of performance.
Quake 3 is gonna be very slow as well, no matter what GPU you put in, because the CPU is holding it back. Minimum requirements for Q3 were an MMX 233 or K6-2 350, which could maybe net you an average of around 20FPS provided you tweaked everything. There were some 3DNow! DLLs floating around but they only improved performance by 2-3fps on my K6-III+ 550MHz, can't imagine they'll help here either.
Arx Fatalis came out in 2002 and required a PIII or Athlon at 500MHz I think, so a K6-2 has no business here at all. Again, K6-2 and even K6-3 is far inferior clock for clock versus PII/III and Athlon when it comes to games.
If you just want to have an overkill GPU in there just for fun though, more power to you. I keep that K6-III+ system and install various games it should have no business trying to run just for fun. Try Morrowind for example, that's an interesting experience 🤣