Automatic detect sets MAX but the FPS are very low

So I play a game called Soldierfront 2.. I pass the recommended requirements. Automatic Graphic Detection detects what your system is capable of handling at a good FPS rate. Well mine set it to the highest settings, BUT it makes me lag soooo bad... So why would the Automatic Detect set it on hgh if it cant handle it, and I in fact have to turn it down to medium just to git 60 FPS.. What could be the reasons for this... If my system is able to handle it.. then whats the problem....

CPU- AMD A8 5600k
GPU- Geforce GT 520 (i know its old, but it passes the recommended requirments)
MEM- 6 GB DDR3 1333
OS- Win 7 64 bit