The 4k upscaling will only really matter if you have a 4k television. It up-scales the 1080p signal coming into your tv to a higher resolution, but not quite at the same level of quality of native 4k content. If you don't have one, or any plans on buying a 4k tv, this feature shouldn't matter much. If you think you might buy one in the future then this might be a good feature to have. Right now I think the only place that actually broadcasts 4k content is in Seoul, South Korea for what it's worth.
The wireless and bluetooth are both good if you plan on using apps to control/manipulate your receiver, or play streaming music over the internet, etc. If this isn't a big part of your listening, then they may not be that important. Your receiver has to be equipped with the components/functionality for bluetooth/wifi when you purchase (unless you plan on personally modding it which I have no idea what would be involved with that). I know there are yamaha receivers that do not come with the antenna as part of the purchased package, but these already have the capability built in.
Really all I look for in a receiver is that it has enough power to sufficiently drive my speakers (which most do for my speakers/environment), and that they have the features that I like. If I were to buy a receiver today it would definitely have bluetooth and wifi as I stream a lot of music. I was eyeing up the rx-v777 while doing some window shopping, but never pulled the trigger as I haven't done enough research. It appeared to fit my wants and needs pretty well. Not sure about the a840. Haven't done enough research.
Judging by your room size (I'm assuming 11x11 and not 11 ft squared...) I don't think you'll have any trouble with power in the receivers that you are looking at. More of a matter of what features are important for you. If the newer features aren't important I'd go with an older model. You could definitely get a higher end legacy model for a good price.
