For the Mac Pro 3,1:
The upgrades sound reasonable, however here's a few comments:
The extra CPU seems like it could be expensive for such an old part. Make sure the extra processing power is worth it to you.
I dont understand why you would replace the existing memory (you write that you currently have 2 x 4GB and want to upgrade to 8 x 2GB). Why not just get an extra 2 x 4GB instead of replacing the memory that's already in the machine. The benefit of filling all slots is very very minor (source).
Replacing a spinning hard drive with an SSD is the best thing you can do for pretty much any computer these days, so that's definitely a good idea
I havent been able to find definite information about if the GTX 570 is actually compatible with the system. But someone in this thread claims that:
All nVidia GTX works perfect. No need special edition, all works in 10.8.2 I have the GTX 770 running in my Mac Pro 2008. In OSX and Windows (bootcamp)
For the Mac Pro 5,1:
The memory configuration is correct. You can't do it any better except by replacing your 2GB RAM modules with 8GB ones.
Again, I can't find any definitive information in the video card, so make sure it's compatible before you purchase.