Rtx 2080 is still more than decent enough to be used as place holder while you save for something else. Im hoping this wasn't part of your initial budget dismissing a new psu. If you can afford a new psu now instead of a new gpu then you should do that regardless if you use an i5 or i7. But if you can afford i7 as well then that would be recommended for longevity since you appear to hang on to your build for length of time. Do the job right at the beginning and prepare for the future i think.
Importance of power supplies shouldn't be ignored. Doesn't matter if you can't see it or has similar price tag to a cpu or motherboard, psus should be treated with more respect than it's usually given.