i7 930 cost more. becuase there motherboard the lga1366(x58) supports crossfire 16x/16x and the memory they support triple channel memory. the i7 860 is a quad core cpu just like the i7 930 but their main difference is that i7 930 has 4 cores/8 threads. your not wrong on what u have noticed because i7 930 is powerful in terms of rendering. i7 860 would be a better cpu if for gaming.
but i suggest the i7 because with their mobo(x58) a 6 core proccesor is cooming which would be a good upgrade path. sooooo i cant explain any further. ive done my research