You could test? In any case you will find thet he licencing fees will tip the point toweards the faster one.
In any case ist hard to say theres other factors at play than just having speed of processor. The overall speed is gratly dependent also on WHAT in average you render is. Some renders are notoriously IO bound then the cpu speed isnt so critical. But bigger memory sizes are citical.
You should really consider the xeon processors they have bigger caches and thus are faster in general, because they tend to keep their pipes full of computation better. The cache size really helps on most renders a lot. However over this theres really no point in xeons unless you put many chips one the board, as they in general have more inter processor communication channels available that the i7's.
However make sure you can afford the FASTEST possible memory.
Leasing is definitely not for you. However i dont know what the situation is over there.
PS: consider a UPS system.