It is worth noting that btcec, our elliptic curve math package, is optimized and faster than OpenSSL when performing operations over secp256k1.
You were not the only one to wonder about specs. I think you can probably assume "Semi-modern Intel CPU with ~4 cores at ~3Ghz".
What were the specs of the machine that capped out at 6 32MB blocks per hour?
I don't think you can easily extrapolate a 20MB block cpu load average by looking at that data studying 32MB blocks under different conditions either.
I did some research and with one of my VPS's(I have some dedis and multiple VPS's )On one I'm paying 10usd a month for 4 cores of Intel E3 CPUs 3.3GHz+ per core and per AUP I am allowed to use all 4 cores burstable and up to one of the cores for at least 1 hour continuously, thus one core running at 80% continuously on an Intel E3 CPUs 3.3GHz should be fine with a 10 usd /mo VPS.
Thus all we need to determine is if a single core 3.3GHz+ Intel can handle a node processing 20MB blocks.