I don't believe there is any volume rate in place at this time. Like you mentioned, if there is a volume rate it might be hard to meet anyway if splitting between paypal and direct checkout. I am 100% direct checkout, and the free month they offered, more than compensated for any difference there may have been in fees.
I seem to be moving along as normal since dissabling paypal about a month ago. I still get requests for money orders, but we had to stop taking them, as they seldom followed through and sent them. I like having one processor for the money and I think of the two DC works for more than Paypal. After all, all of the sellers that like to pay with paypal when they make purchases can simply use their paypal debit card on DC.