Dell L702x low Windows Experience Index score on Processor

I have Dell XPS 17 L702x with i7 2670QM @ 2.20GHz CPU. Somehow i am getting very low score on WEI which is 4.5. I googled a bit, and found that most people that have same laptop score on avg. 7,4. The thing is that my computer doesn't work smoothly. It kinda stutters sometimes when i play games or have many browser tabs open. That is why i started researching the problem. 
Any ideas why might this index be so low compared to others?