A:Answer We are unclear on what is meant by "Classic Mode", that is not a setting on eero. To get gigabit speeds wirelessly these Pro 6E should be able to give those speeds wirelessly, depending on if your device can go that fast of course.
If "Classic" mode means putting the eero into bridge mode, that could, and likely will, reduce the wireless speeds capable on the 5 ghz bands. It should still be pretty good/fast though, just not likely to 1gbps speeds.