You should drop the 4850. 4xxx cards have poor hash to power consumption ratio. Even with your electricty cost I think you're actually losing money on the 4850
Hmm I guess I will return the 4850 to retirement.
I'll have to do some calculations to see just how it's costing me.
Out of the top of my head:
At 70 Mh/s you have an average production time of 65 days, 13 hours, 57 minutes per block with this weeks difficulty. Assuming it remains at that level (which it won't), and your card is about 200W on load, now let's be nice and say 150, you'd be at 3.6 kW a day or 234 kW per block. That's $15 of electricity per block. Well, I'll be damned, that's some cheap juice you got there.