For a mono bullet the 168 TTSX BT worked out the best for me on elk sized game when fired from a 30-06. It seemed a better match to the 30-06 than the 180 grain version. I used that combination on one of my Botswana hunts for critters up to the size of eland (app. 2,000 lbs. on the hoof). It worked quite well. I had previously used the TSX and found the TTSX to give more reliable expansion.
I have taken a fair number of elk. A broadside shot on a calm cow is not a problem, but penetration can be a big deal if a "less than ideal" angle shot is required. I now mostly use the Nosler AccuBond bullets for elk. I used the 180 grain AB bullets on the same African game as the 168 Barnes (out of the same 30-06) and prefer them slightly to the TTSX BT 168. I have two elk hunts planned for this season and intend to use a 300 WM with 180 grain AB on one and a 280 with 140 grain AB on the other.