Hi, I'm looking to replace my 21.5" iMac of the last 6 years, and I understood there are a number of similar 21.5" models, including one with a 4K screen. 27 inch is out of my budget. I'm not what you'd call a "power user," a lot of Internet, writing, ocassional photo editing, etc. May use it for streaming as well (we have an iPad an plan on an Apple TV maybe). Any thoughts?