I didn't rewire with painless, but if it's got door jamb switches and what not, hardest part is getting all the wiring tucked up under the dash, and I'd assume if you have a domelight, the domelight wiring. Making it functional/decent looking was darn near impossible, I'm still not happy with it around the column, too many wires, not enough room to make it look "clean".
I did it with no interior, so it was pretty easy, still time consuming. I'd not want to tackle it without at least stripping the dash to bare metal. Cluster, dashpad, lights, etc.
Guess the only difference between painless and factory is what "options" the painless kit comes with, although I'm guessing the circuit count is what gets you in the ballpark for your options.