Blood DK PvP Question

[:1]I have an 85 Blood Death Knight, and have been full time flag carrier when playing with my 2-3 friends (one rogue doesn't always join us). I have no problem with survivability so long as I'm not being stacked by more than 3 enemy players. I don't need a healer, (however it takes a huge stress off my hands due to the button mashing I use to stay alive) as I can use Death Strike to heal 20k, use Rune Tap to heal 10k, use Rune Tap again when it procs for around 15k, and then sacrifice my ghoul-minion-thing for around 50k. I have about 160k health with a stamina buff from other classes, and about 3500 resillience. Keeping all that in mind, I have nearly 0 mastery. Someone scolded me last night in a battleground, and I have to say, they may have been correct. Should I forget about resilience and go gem all mastery and grab the off-set pvp pieces that mastery instead of resilience? Mastery for Death Knights provides a huge damage shield when I use Death Strike, however my understanding is that it only protects from physical damage, and with less resilience I will overall be taking more damage when I don't have the shield up.

If someone could provide me with a good answer, and explain to me why they think that, I would be very greatful.

I'm on Bleeding Hollow (Alliance w00t), so if you're on it too or in my battlegroup, message me ingame, character name Âlexander, and I'll be happy to mess around and crap on some Horde :P

why drop resil for mastery? you can have the base resil from your pvp peices and either pick up the mastery/resil peices and reforge your crit --> mastery its higher on your priority list and will also help your frost spec out.
Don't gem mastery. He is right though you need to reforge for mastery. Frost DKs in pvp reforge for mastery once they hit the 5% hit cap, so reforging for mastery will help both of your specs in pvp.

Even though blood shield only abosrbs melee damage, casters hitting you add to the size of your blood shield when you DS, so your overall mitigation is higher. This is assuming melee classes and casters are hitting you at the same time.
Alright, thanks a bunch guys. I'm getting into arena soon, I want to be as unkillable as possible by the time I start :P