I disagree with you regarding CPU load
Maybe it's just a problem I have had because I tend to run p2pool nodes with a lot of hashrate. I also always do SSDs, so I've never seen the HDD->SSD improvement.
How many clients are connecting to your node? The difficulty of each share submitted by a client should be commiserate with its hashrate. Unless you have >1000 clients connecting to your node, I do not see how your CPU would be a factor. I run a lowly Xeon X3450 and the sucker is only pushing a 15 minute load average of 0.31.