Is my pc too slow for playing 720p and 1080p without gpu acceleration?

I have a problem with 720p and 1080p Mkv-s in Vlc. While i m playing 720p and 1080p mkv is in vlc 2.0.6 they are stuttering and lagging on some part of the movie. When i turned on the gpu acceleration the stutterin and lagging is gone. then i tried the same filles play in several other players with and without gpu acceleration if they had the option for gpu acceleration.The players were MPCHC,Gom player,KMPlayer,PotPlayer and SMplayer an there was no stuttering on same part of the movie as in VLC. So my questions are:
1. why are the mkv lagging in vlc when is gpu acceleration turned off but they are not lagging in others players with gpu acceleration turned off?
2. Is my Cpu too slow for playing 1080p and 720p mkv? or is it just a problem in vlc?
3. Which of this all players schould i use for video playback and how scould i configure them for best settings?
Please answer to all 3 questions!
My pc configuration is: CPU- Intel Core i3 2120 @ 3.30GHz
Motherboard: Asus P8H61-MX R2.0
Gpu: MSI Radeon Hd 7750 1GB DDR 5 (R7750-1GD5/OC)
Ram : 8 gb
OS : Windows 8 Pro 64-bit