My first computer had a 1.8MHz Z80 in it, ~1980.
Heard people say the same about 10MHz, 100MHz, 1GHz, 5GHz...
Clock speed got out of hand and things are being re-balanced towards the "brainiac" approach of more work per clock. That doesn't mean that more GHz is bad, and it *will* start creeping back up again.
One thing you can be certain of, when they do come out there will be threads like this with our children moaning "I had my 5THz CPU on order for weeks and still no sign"
BTW, Scan are now showing 5000+ and 5200+ OEM in stock (at the risk of going on topic).