It depends on clocks and voltage needed. Even if your CPU and GPU both end up with an overclocked TDP of 200w each, you still have head room...even if both are 250w.
It really will come down to what fans you want to use on the rad and what pump you will be running. I almost always consider a 10C delta-T when offering suggestions as that is pretty common and budget friendly. This entails a 1.0-1.5gpm flow rate and around 1500-1800rpm fans over that rad. So, with slower fans, you might be dissipating 475-525 watts (I'd have to look at Skinnee's graph for fan speed at 10C delta).