Worth mentioning that there is an open-source port of the X-Ray (S.T.A.L.K.E.R.) engine that compiles natively on Linux and works on x64 platforms without a 32-bit compatibility layer, OpenXRay. It currently supports Clear Sky and Call of Pripyat, and development to support Shadow of Chernobyl is ongoing. The repo claims performance is improved compared to the original binaries, but I have not tested this myself to confirm.