I always get it slow since I am doing it myself with a dildo, and it's hard to go fast and not get tired arms LOL. One time I tried a machine and the fast, ass-pounding I got was just what you described "Intense". I got rid of the machine the next day because I loved it so much I knew I could never go back to slow as long as I had it and being reamed like that every time would cause my ass to fall out after a few months. But even now I long to have that experiance again.
I find that the line of "I just can't take it anymore, it's just too much pleasure and stimulation to take." is something you have to allow yourself to be forced past at least once in your life. I wouldn't be suprised if you have already done this but I would suggest you let him completely tie you up and after getting your bum warmed up, pound you relentlessly no matter how much you beg him to stop to give you a rest. That wall that is making you want to stop could be the best, most intense, orgasm in your life.