@kyriacos I like the design, but I don't think cropping the text of the headline is a good idea. That part of the banner should be prominent and immediately understandable. People may only get a split second glance at the poster as they walk by or drive past, and you want them thinking "Steem Fest!" not "Huh?"
The stereotypical sizes only exist because they are requirements for different mediums. For example, if you want to use the design on a billboard you should use a specific artboard size, 3048mm x 762mm (25% of full size) with minimum 300dpi for photoshop.
Popup banners and other mediums will have their own dimensional requirements.
It looks like you used a bitmap image (the photo backdrop) so the resolution of your original image will define the largest medium you can print to without loosing quality. That said there are some tricks you can employ to minimise definition loss on resize. Google "Fractal Interpolation with GIMP" if you are interested in a free solution.
I understand your points. I have been a designer for almost 2 decades. My point with the title was to create something that gets the attention. a visual play. almost create a nuisance. I am not a hardcore designer. always going for the artistic part as well.
as far as the pixel quality. if that poster was chosen I would definitely pick another high resolution picture. this one was just for sampling.