@DB
but white balance is always a problem, even using Custom WB with my Lastolite 18% Grey collapsible card. Different lenses + cameras will almost never synchronize custom WB, so you're forced to color correct big time.
My advice is to ask at the store if you can also purchase Dichroic Filters or large CTB gels to place in front of the lights. Believe me its much easier in post when you shoot as 'neutral' as possible.
The colour of coatings and UV filters etc all have an effect on WB, uniform lighting is not enough, a preset if good, as at least you are in the ball park, and you are consistently off (one fix, unlike AWB) manuallyWB off of a unfirom source is even better, I use a greyscale QPCARD in some header roll, which gives me a much better chance of matching the shots when used with either preset, manually input or manually balanced WB.
The bigger problem for me is not WB but expsosure matching. Even a constant f2.8 lens will vary its T-stop accross the focal length, two different constant f2.8 lenses (such as you 24-70 and 70-200) will be even further out. The f2.8 is not actually absolutely constant.
ISO for ISO, light for light, shutter for shutter the cameras should be pretty uniform, aperture is not likely to be exactly f2.8 on any given lens at any given focal length at any given time, and the T-stop is never going to be the same between to optical designs, or even the same lenses of different ages (dust etc)
But as far as WB goes, get both cameras as close as you can, and keep them consistant and you have a fighting chance. Costly filtration is not going to do much more than add more to the mix, cheaper CTB gels are the way I would go.