Well, I gotta ask this question before answering one aspect: Is this build good for what?
If you like having a lot of health(most out of all builds), being able to tank, and dealing a fair amount of damage, then yea...this is a good build.
I'm not sure if 4 gap's good enough for all that, but you can use this link to find out for yourself.
http://www.nivlam.com/sp/
And for lvling up the Cold Mastery, I say no. You're already Pure Str so you already have a high amount of Phy Def., take fire as main and light as your sub and you'll be fine.
Read this if you want info about builds and such...
http://www.silkroadforums.com/viewtopic.php?t=19902