Well, I don't wish to sound like I'm having a "hissy fit". (Could you define that please? :O) )
I personally think you must take the verses of 1 Samuel and Numbers for what they say. They are plain and consistent with our understanding of God. In all other verses I think God, our loving Father, grieves with His creation. But this does not negate carrying out His sovereign will which must be done because of who God is.
God perfect plan made Saul king to carry out His divine plan. He was sorry He made Saul king but God did not cease to carry out His will. God could have told Samuel on the day He told him who to annoint but it might have seen pretty strange to say "I'm sorry I made Saul king." while Samuel was crowning him. Even from your Arminian perspective you might as well throw "those whom He foreknew..." out the window for you would be saying God did not foreknew Saul or how he would act. And I don't think that is what you're saying at all.
To me this whole Open Theist talk boils down to not having a systematic theology in place. You carry this to its natural conclusion and you might as well be worshiping the Greek gods who make mistakes and have human traits.
Which is exactly what I have done. I think the danger lies in trying to explain the paradox, i.e., that God's plan made God sorry. If indeed God had foreordained and predestined that Saul was going to be a bad king, then God would not be sorry that Saul was made king, as it would have "pleased" God not only to make Saul king, but to make him a lousy king to boot.
OTOH, if God didn't know that Saul was going to be a lousy king, then it would be pretty plain as to why God was sorry that he would have made him to be one.
Since God knew all along that Saul would make a lousy king, so much so that he would have "repented" of his decision to ordain him, then there is something else at work here that is difficult, if not impossible to properly convey, something beyond our understanding of the words predestine and sorry, something beyond the words foreordain and regret.
Here's one for you...
Jesus wept.
Think about the implications of that for a while.