How large is your card? On a 32GB card I have shoot around 1,000 raw images. Is that enough for a single event. Costs are around $150. Consider that 1,000 images is the equivalent of ~30 rolls of film. Back in the day (ancient history) slides plus processing cost between $10-15/roll. Digital equivalent of a roll of film (36 exposure) is only $5.
Double the card size, you will double the number of images. Are you using the vertical grip? If not, the battery will die before a 64GB card is filled. A 128 GB card will outlast both batteries in the vertical grip.
If you are still worried about filling the card try setting the camera to use automatically switch to the second card once the first is filled.
Yup, using 32GB cards. I switched my first card with about 100 pics left on it and I filled up the second one. We tend to shoot quite a lot (in the 3500-5000 shot range). Not using a vertical grip although I'm curious if it might help me with the 70-200. I tend to use it a lot in portrait orientation and my arm was pretty sore by the end of the ceremony.
I have the vertical grip, and aside from the extra weight and bulk in the bag, I really like it. The vertical shutterbug is a really plus and I like the larger size.
If you shoot 3500-5000 shots, how often do you need to switch batteries? I tend to get 1500 shots / single battery (straight shooting, no viewing, no tracking with a supertelephoto lens).
It's 3500-5000 between 2 cameras not just one. My wife and I do it together. 3 batteries normally covers me.
Canon 5D Mark II, 50D, XSi, 24-105L IS, Canon 35 2.0, Sigma 10-20, Tamron 17-50, Canon 50 1.8, 580 EXII, 430 EXII