For "portraits and travel" I would simply change your lens setup by selling 70-200/4 and getting 70-200/2.8IS and adding to it 24-105 which can be found these days brand new for a crazy price since so many of them on the market being sold as kit lenses. In terms of $$ you will be in a better situation than just purchasing a new 24-70/2.8. In terms of travel you will have a better walkaround range 24-105 for travel and a great 70-200/2.8 portrait zoom lens which is the best zoom in this focal length (lets face it - 24-70 is not the most preferred portrait focal length out there). With time, for travel I would add a 35L or a Sigma to your travel kit and then you're golden. But if you do travel shooting as a pro and you are OK with spending almost 3 times more for 24-70 with a better IQ then yeah that might be a better option. I'm not sure how often you will be using 2.8 for travel though. I guess it depends on what exactly you're shooting while travelling.