20 'C Tthermal margin is plenty to spare for more overclocking. The 212 Evo won't be strong enough when you get to the big clocks though. Big air cooler or dual radiator loop is what you need for some serious clocking on that CPU.
Meant to reply to that not mark as best answer. Oh well. When you say dual radiator loop is that a 240mm radiator? Like the H100i?