Depends on what you're rendering and if the 'Used Physical RAM' is always breaching 75~80%+ then yep time for a 24GB kit.
Q - Why are you going from Corsair to G.SKILL?
Why not the CMP24GX3M6A1600C9? or the cheapest F3-10666CL9T2-24GBRL? The Corsair will save 10~15+ minutes on a 4 hour rendering.