I wasn't really expecting much from doing this, but I had an old Crucial M500 960gb SSD lying around from an old laptop I gutted. Decided to plug it into a SATA-USB 3.0 adapter and try it on my XBOX. I immediately noticed a massive difference in load times when I moved the game from the internal to the external SSD. Times to enter buildings/subway/etc is 5 seconds max, and fast travel is about 15-18 seconds.
I didn't do a control test with the internal HDD, but I know just from feel that it's a lot shorter. I would always have a second 'tip' pop up in the loading screen and with the new one, the loading image pops up, rotates a little, and then I'm loaded in. Not the most scientific I know, but the difference is very, very noticeable even without having the actual numbers. I recommend anyone on console who are unhappy with their load times to give this a try if they can get their hands on a SSD.
Just figured I'd share.
edit: Just did a little test. Did it 3 times.
HDD: Fast travel from Sanctuary to Castle - ~38 seconds from confirmation click to fully loaded screen
SSD: Same fast travel and parameters - ~16 seconds.
Not bad