You are forgetting about other mobs in ur pushing calcs. When you finish the wave (in 258 case kill the boss), all the remaining mobs on the map will fly backwards and die. Or in the case it's back as against a edge and was close enough (depends on fly back) it will fall. If that mob falls down it counts as a push. So if ur gonna go all out pushing you will have to make sure you watch out in the first and second bulk waves where you only kill a few, in the case there are mobs that can fall. Also on the boss wave there are a few mobs that fall (Nimba north of boss in middle, and Nimba at left side. )
Anyways dunno about ur exp rate there. A 10% reduction from pushing reduces ross' exp by almost 10k (65,535 to 55,660) on x3.
65,535 - 55,660 = 9,875 exp. (10% of max exp.)
Thus multiply it by 10: 98,750k exp on x3, with t3, and member. and guild buff.