If outright performance in a GT package is required, the Mustang GT350 dusts the M4 with lots of money left over for mods.
If you want a prestige car that isn't a glass cannon, the RC is where it's at. The M4 continues in the long tradition of great cars when they're working, but that isn't going to be as often as a comparable Lexus.
There's an orange one rolling around here. Looks pretty good but for the front end, which is still pretty over the top.