The screen is only 220 nit... that's abysmally dim. For comparison, the Samsung Series 7 17" is 300 nit.
Your info is wrong. The average max brightness of the screen according 259 nits according to notebook check who reviewed this specific laptop with the lowest of the nine sections was 240 nits. The highest section is 290 nits.
Just because laptops use the same panel does not mean they have the same lighting.
--------------------------
Furthemore samsung series 7 17" doesn't tell a whole lot about your laptop there are different models of samsung series 7 and they will have different screens. Furthermore manufactures have been known to switch panels for monitors for the same model or a 3 month referesh down the road.
--------------------------
What is far more important is how accurate the color, the real contrast ratio, and the viewing angles. While still a tn panel, the 1080p tn panel used in the y500 and y580s not a bad tn panel achieving very close to srgb and having a 450:1 real contrast ratio, for comparison the alienware m17r4 panel is about 580:1 for contrast ratio.
--------------------------
If sli doesn't work at all you are getting about 75% of the performance of the gtx650 normal desktop card (note I did not use the ti in this example).
If sli scales perfectly you are getting about 85% of the performance of the gtx650ti desktop card (note in this example I did use the ti).
Use these numbers and multiply the correct percents to get an idea
http://www.anandtech.com/bench/Product/681?vs=680