Well, forgive me for disagreeing, but Calvin and Arminius were not preaching different gospels. I'm neither, by the way. That may be difficult for some on either side to grasp.
That said, I would point out to you that Spurgeon disposed of the argument long ago. I saw it posted on this board, I think, not long after I joined, and checked it out for accuracy. Can't remember who posted it, however. It is worth repeating.
Anyway, Spurgeon said he reads that God is sovereign and he must believe it. And he reads that man is responsible, and he must believe it. He went on to say, at first glance, these appear to be two parallel lines that can never meet, can never be resolved. But, he concluded, they must, because they are both true according to Scripture (I'm not going to argue with an intellect the likes of Spurgeon) so somewhere in eternity they must meet.
That's good enough for me. If I'm not meant to fully understand how a sovereign God can know who will be saved, and yet hold man responsible for being one or the other, then I happily conclude that it a mystery I will understand on the other side of this life, and choose not to let the dichotomy bother me, or influence me to think that someone who has decided it is one way or the other is right or wrong. I don't believe anyone knows. Spurgeon didn't, and it didn't bother him.
I think endless discussions, which tend toward useless efforts of proving a brother or sister in Christ on one side or the other as being a "heretic," are destructive to the body of Christ, and the concept that this is "two gospels" is even more so. I bow out now, leaving both sides to their destructive interfaces.