Thanks @manji for pointing that one out. Sorry @dimsk but I just want to stay on topic on my questions and you advising on the power consumption factor wasn't helping answer my queries.
seems your spec doesn't need to upgrade, its good enough for multitasking. your lag issue caused by your CPU do the mining through NH.
Yeah, I have done disabling the cpu mining on the setting of nicehash but still getting a little laggy. Also, I have used a CCminer, its not that laggy like nicehash but giving me lesser hashrate than nicehash.