I have used both, so I can tell you:
I went through two sets of MSD wires in four years on a street driven car that saw no more than 500 miles in that time - obviously, I rarely drive the car. Despite this, the MSD wires had melting boots, cracking wire sheathes, breaking wires, you name it. I would never buy another set.
Switched to Firecore 50's about two years ago, and couldn't be happier. Notable improvement in performance (spark) over the MSDs, and after 200 or so miles of stop and go driving, not a sign of melting boots, cracking, etc., etc. (which I would expect to see for so few miles) They are so much better than the MSD wires, it's not even funny.
Not trying to pump up the rep of a member here, but they are simply a great product.