It's actually not too small at all. Some things are small but I can make everything out...if I need some text in safari bigger, I just cmd and the + to zoom it once although I haven't had to do this yet. I actually like this a lot better than what Apple was letting you do. I only have the brightness up about 33%...raising it more makes things very easy to read.
UI lag isn't any worse...I expected it to be, but it's not. Battery life indicates to be as good as it was before doing this. I am currently (and have been working for a while) in 4-5 safari tabs, 30% (maybe 35%) brightness, Outlook 2016, VPN connection, and maybe some other things. I'm at 81% battery and it says 6 hours 56 minutes left...If anything, I think it may be better than what I was seeing last night - but then again I think I was still indexing and downloading photos in the background.