Using unshielded RJ45 with shielded Cat6 in a server cabinet
Since you have STP, you should terminate them to gnd for RF improved performance. 

Signal Integrity and Group delay times vs f for CAT6 signals are improved with a grounded shield rather than,a floating shield that couples the leakage of all signals to the ground.  But this property is depending on cable lengths up 50m or 100m in future drivers.

Avoid cable kinks and shape bend radius smoothly > 4Dia and avoid shield strip > cable dia. at ends.



While shielded components do cost slightly more than UTP, the increased performance and reduced testing time can ultimately lower the total cost of ownership. 

The next generation cabling systems that perform beyond 10 Gbs transmission speeds will require shielded cabling and components, which makes STP systems more future proofed than UTP.

The result is similar lifetime costs for both STP and UTP systems.