Couple of questions regarding central a/c system replacement, mainly regarding variable speed

We live in the northeast so it gets hot and humid. 2,500 sf colonial house with only 1 zone. thermostat and return are upstairs, along with 6 vents. downstairs only has 3 vents and is therefore hotter than upstairs. We've survived over the years and it's not too terrible, but definitely noticeable.

I was considering a variable speed system when it's time to replace the old one (which is definitely coming up soon), but then got to thinking that given my setup, is it not worth it (i.e. the system is still likely to turn off too often as the upstairs will still be colder than downstairs)? Or might it still be worth it as it might balance everything out a little better simply by runner lower/slower at times?

And no, it's unfortunately not easy/practical (and too much $) to add another zone, extra return, etc...

Thank you.