The Classic Shell Start Button is dynamite on Windows 8. You don't need it on 7.
I have XP, 10, and 8 on separate partitions on the same computer, and they all work well. I upgraded 7 to 10 because I wasn't using it anymore. I see little benefit in installing a legal copy of 7 on your other SSD, plus backwards installations usually don't work well. The architecture for Win 7 has been improved so heavily by now that I doubt that Win 7 will run well on your rig.
The program I still with here having already tried out the Hyper-V option would be the latest VMware Workstation 12 Player which is free for home use and won't take up that much space for the installation itself. Then you simply opt for no larger then a 60gb VM for 7 to run on. I even upgraded a 7 VM to 10 lately to see how that would go.
Want to try out some new Linux distro some time? WS 12 will cover that as well. And if you have enough system memory you can even having multiple VMs running together while that would be mainly seen on the desktop. VMs can also be backed to other drives and when run you simply select the moved option in case you need to free up drive space on the main itself.
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