I honestly wouldnt worry, I saw my old 5900u go up to 79C and sometimes higher.
I used to have a few problems with far cry with my 5900u but patches sorted things out for me.
Have you installed any patches for far cry?? If not try 1.1 patch and see if it helps.
The lag your getting is probably normal i remember it on my 5900u running reasonably well with some lag as its a very intensive game.