Are the cpu speeds that we enjoy today a bubble?
No but you could say the speed increase we've enjoyed over the past decades will hit a brick wall. In so far it hasnt already. And moore's law is running out of steam too. IIRC on some chips we are down to feature sizes that are just a dozen atoms wide, transistor size is approaching atomic levels. It just doesnt get smaller than that. We are not there yet, still a few shrinks that are probably feasible but the end is in sight.
Even if speed increases hit a brick wall (which I disagree with), the total computing power on the planet will still go up, as it has, at an exponential rate.
Even if asics hit a "brick wall" in terms of process (at 28nm) and then hit another brick wall in terms of design optimization, the hash rate can still go up significantly due to parallelism. More of the most efficient asic will be brought online. More efficient hashing power will displace less efficient hashing power. Yes, the rate of increase in the hash rate will certainly go down - it's unsustainable. But hash rate will continue going up for a very long time, unless bitcoin price crashes.