Should I use Intel SATA Controller Driver instead of Windows 8.1 Inbuilt Driver to get best speed for my SSDs ?

[vikbot]

I'm attaching screen shots of benchmark result..

Samsung 850 Evo 120 GB -

Samsung 850 Pro 512 GB -

So, what you guys think ? Am I getting slow speed by using windows default SATA Controller Driver ?

 

[CountMike]

There's nothing slow there, those different results are at the level of statistical error and no way that it would be noticeable at all !!!
BTW: You are using wrong benchmark, it's made for HDDs not SSD.
http://www.techspot.com/downloads/6014-as-ssd-benchmark.html is much better at benchmarking SSDs.
Another thing, you didn't benchmark 4K and 4K-64Thrd, they are way more important for work. Speed you were checking is for copying files and can wary a lot in everyday use depending on file size and type.