I have an i7 and lightmass uses all of my cores/threads when I build lighting. The i3 is probably going to be as fast or faster than the fx-6300 which is based on 2-3 year old technology. When I bought my i7-3770 I A/Bed it with an fx-8350 and at the same clock speed the fx-8350 was only 60 percent as fast as the Intel cpu when baking lights. I would definitely go with the Haswell board/cpu just so you have the updated hardware.