This might be more about what your trying to do with the restoration and how your planning to use the car when it's complete.
Your body shop/paint mixer should be able to achieve the proper color if you choose paint. I've seen some pretty comparable colors using powder so the color of either might be a wash. You can tell the difference as paint vs. powder has a different look but either way the colors should be close.
Some might argue that powder is slightly more durable so if your going to run up the miles on the car that might be the way to go. Repairing a chip in powder is tougher as it's a slightly different process than repairing paint. Matching the color of powder with paint can be tricky too. Your gonna chip and scratch the frame during re-assembly so that's another thing to consider.
Personally, I'd use paint. There are some very good products out there that will hold up to lots of use/abuse and are fairly simple to touch up down the road.