Chandler, you could also check if the brand of SSD has a Migration tool that does all this for you. It worked for me with Samsung SSDs and I believe Intel has one too for that. I succesfully pulled both a 40GB Win8 (yesterday) across from an iron disk to a Samsung SSD via their migration tool and zero issues. And I have done it in 2012 with an Intel drive as well, though that was SSD to SSD(X25-M to 520).
The source drive should'nt matter though, what matters, is only that the old drive's current "used size" doesn't exceed the new SSDs total space. Kinda goes without saying, but with small SSDs, just make sure you are not close to the limit either, best to leave 20% free on them for comfort imo.
If you have a laptop, keep the old drive in it and buy a 2.5SATA<-->USB2/3 thingy, that works too for that purpose.
Edit: To clarify, this essentially copies the whole OS drive to the slave SSD, but in a way so it works when you then afterwards swap the SSD drive to become the OS drive. The SSD is completely wiped in the process, so don't assume a little stuff can remain on it, even if there is technically room.