Not really to related to your build, which seems to be effective, as ive tested

but thought i might as well submit the beast build i run, which seems to work quite well.
Attributes
16 beast mastery
9 expertise
11 marksman
4 wilderness
Ok so as you can tell its primary beast, but the thing i like about it is as a ranger using your bow, your still effective.
Skills
incienary arrows {E} -the reason i have wilderness at 4 is because at 3 WS it burns for 1 second, so at 4 it burns for 2 seconds which is really all that is needed because if your using a short bow like i am there is usually the right amount of time to keep them burning non stop while it is running, also making it 3 second burn requires that you really put your wilderness quite high.
Pen arrow- This was the skill i found worked the best as "your" damage attack, sure brute strike would work alittle better but this build really is about feeling your actully not fully relying on your pet

yet having your pet at its best.
Disrupting lunge- This attack really does shine for me as a beast mastery skill, with half the recharge time of distracting and adding damage instead of limiting it. However the problems with it are, you cannot really time it to a skill, like you can with distracting and it also only interupts skills not general actions like dis does.
Res sig- Although some people may disagree i think everyone should equip this skill, athough my play ground is mainly the random arena so thats probably why i have this opinion.
Whirling defense- This is my only protection for myself i bring, it really only counters warriors, well the ones that dont bring wild blow but i still think it saves me afew times, with people changing targets when they see, hmm this ranger seems to be evadeing me
Call of haste, Charm and comfort animal- While i really like call of protection in pvp not many people seem to attack pets and with charm animal healing 110 and reviving to 61% health, it doesnt seem to important to bring it over haste, also it really is a joy to see a monk or something trying to run away from a huge bear running twice as fast

Hehe also, good pets to bring are big ones like moa birds and bears, cause it really is funny and makes a round worth it when you see a warrior get stuck behind or besides them, and just sit there for 30 seconds not understanding that they need to take control themselves
But yeah, like i said not really topic realated, but if it can maybe point someone in the beastmastery direction it is sure worth it for me.
Anyway nice pet build you got there with using balthzars, and sure is fun to play