InDesign CC performance is more affected by having large amounts of RAM and the SSD than it is by the GPU you have in the machine. Sounds like you have a monster machine at home compared to the Mac Pro at work and it is the RAM and SSD that is making the difference. You don't mention how much memory you have in your Mac Pro, but I would look at memory and SSD upgrades to your Mac Pro before a GPU upgrade.
I agree with Mark on this one.
The SSD moreso than the Ram. If you want to kick it up even further, you can create a 16GB RAM disk and install the apps and see how that does.
Now that InDesign has 64bit version, it'll be interesting to see how it utilizes the memory/CPU. I was disappointed with how little Illustrator 64bit utilized the different cores of newer processors and doesn't take up a whole lot of memory either.
I only have 6GB of RAM in the Mac Pro, but I ordered an upgrade to 16GB. I will see if that makes a difference.
Thanks for the advice.