Sorry I should have been clearer, when win64_cryptonite-qt_14091021 is just running as a full node verifying blocks it uses more cpu than my blackcoin client when it stakes, so it's verifying and sometimes creating blocks . I've seen it get upto 25% so my worry was that your M7 PoW was more difficult to verify than the standard bitcoin sha256. It should be possible to run nodes on very low spec machines to encourage as many people as possible to run xcn and leave it running in the background to increase the network security.
Well obviously the M7 PoW algorithm is slightly more difficult to verify because it uses 7 different hashing algorithms instead of just sha256, but it shouldn't really make a noticeable difference. The CPU usage spikes that you are referring to are probably the times when your node is seeding other nodes, particularly when it has to generate a "slice" of the account tree. That's why "slice sharing optimization" is the top priority for the core code development right now. The plan is to keep a second copy of the account tree in memory which is set 10k blocks in the past so that those slices can be served up almost instantly and wont have to be generated on the fly when they are needed.