Decware does a great job of running a pentode tube as a SET. Given your speaker efficiency, should sound wonderful. I have their integrated, but Decware also has monoblocks. I am amazed at how good 6 watts/channel can be. They run a el-34, but you have tube rolling options. For example, ran some KT-88's to up the power but this did not do well for the sound. Sorry, sounds like you had it dialed in and this is another direction.
Otherwise, I would say go with the 845 in SET. Given your room size and speaker sensitivity, I would be tempted also by a 300b SET.
Good luck.