When processing a small number of spectra, CLASS90 will be quick on whatever kind of computer. Now, if CLASS90 users needs to process dumped spectra, they should then be prepared to use a powerful computer (with lot's of RAM to avoid swapping) and to wait during processing, whichever software (in particular whichever version of CLASS) they are using.
Moreover, flexibility is favored in CLASS90. This means that the same things may be done in many different, more or less efficient ways. It will take time to the CLASS90 community to learn what should be or not be done to ensure efficiency. For instance, loading with the LOAD command (see below) on a laptop is probably going to take a while (if possible at all due to limitation in RAM memory). However, this possibility does not even exist within CLASS77.