I use Predator and luSH101 in "huge" mode all the time and love it (27 inch monitor, don't remember the exact reso at the moment....I'm not on that computer). But I agree the ability to select a size that fits your needs is obviously the most practical solution.
It also depends on the plugin.....simple delay plugin or complex synth.
Did you have a particular plugin in mind when asking this question ENV1 ?
Oh and for the record I wouldn't mind if every plugin had a GUI designed by ENV1..........
