45nm was a huge clock speed jump, with 32nm improving further still, so it's possible that a hypothetical 32nm Pentium 4 could have clocked to 6 GHz or higher on ambient cooling. A 6 GHz Pentium 4 would still not have been remotely competitive with Core 2, let alone Nehalem.

Aye, but that was the tradeoff they made. They chose a uArch design layout that prioritized clockspeed above IPC. I'd even agree with you, theoretically it should have no problem hitting 6Ghz at the smaller nodes. But ultimately clockspeeds are a poor substitute for better IPC. Intel has face planted itself against the clockspeed wall twice now, first with Netburst and then a second time with Raptor Lake. If Intel hadn't been juicing the voltages with a half-dozen types of overlapping boosting behaviors to try and eke out every last hertz the degradation issues wouldn't have happened. Alder Lake had absolutely none of these problems.

I do have to wonder what comes next though, ultimately Zen is still just a uArch family. Intel and AMD both will have to figure out new massively overhauled designs at some point and I'm wondering how many more times that can happen given the constraints of x86 itself. FRED seems like the sort of thing needed to throw off some of that deprecated legacy baggage but I'm not an engineer to really know how many other things similar to FRED are possible with x86.

As per the clockspeed improvement it seems a safe bet. Just remember there's now 50% more cores using the same power budget, plus any additional cache size increases. I'd gladly take the same clocks with a dozen cores to be honest. Whatever AMD does for the sorely overdue IOD overhaul will also affect the general power and thermal budgets though, too.