In my not so humble opinion, if any aikidoka whatever their rank, is inflicting pain on purpose then he should be disciplined by the head of the Dojo. If it is the teaching sensei, I would leave the mat and complain to whatever organisation this persons belongs to. If the pain ends up in actual damage, then I would consider legal action. It is violence and not harmony therefore not ``Aikido''.
Then again, there is this riot police course given by the Yoshinkan Hombu where I am told people do end up with blood on their gi. Generally not only thier own.
It's all a matter of what you signed for. If the dojo state that they are full contact and require hard and painfull training then if you go there don't cry if you are hurt. It is not how I want to train but then again I am not training to become a hard combatant. However, I do train in a pre-war style which are known for being ``harder''. </macho>
As for frustration, we are all guilty of it. I find that having a routine to get onto the mat helps me put a barrier between the world outside and the dojo. It works for me, it may not for you.
Should you (David) talk to your partner? Sure, you should. Talking is the only way missunderstandings are cleared. Try to understand him and make him understand you... It's all to do with harmony I am told ;>