If I were in your shoes, I would use the 140 TSX. As has been stated before, the lighter weight TSX bullet acts like a heavier bonded bullet, like comparing the 140 TSX to the 160 AB. Also, IMO, I believe the TSX will out penetrate the AB if/when hitting the same medium. When shooting thru the shoulders of African game, penetration is the key behind shot placement.
I hunted the EC in 2010 and will be doing so again in June. I took two kudu on my last trip, one at 168 yards and the other at 225 yards, with the former making it about 60-70 yards and the latter about 10 steps. The kudu was the farthest any of my critters made it, including a black wildebeest that stumbled about 25 yards after taking a 180 gr TSX from a 300 WM at 271 yards. The remaining critters on that trip were all little guys, so not very comparable.
Good luck!