a 454MHz ARM9 is two orders of magnitude slower than a HP 54600 with a 10MHz 68000
In due fairness this is not correct.
You all know that we're talking about realtime equipments with limited resources. Of course we can fine tune indefinitely but there's a moment when we have to stop or when the proc scheduling can't accept any other task!
These are not academic projects. These are commercial products.
This theme can go on indefinitely...
We usually see discussions here about BW upgrading (all types of venues) and always discuss the theme from the analog part of the scope but, for sure, many times the problem is simply the processing power to crunch the same functionalities/options at a higher speed.
But, in the end, it's all about $$$