I'll look into the suggestion (more pressed for time than anything else).
The gloomy outlook on Mac's came from seeing a MacRumor's site with "Don't Buy" for all but on Mac model, the other being "Neutral." (I'd hope for more USB ports on a MacMini and, well, the usual "faster.") Macintosh has entered the realm of "commodity" so I don't expect new features, just more capacity (disk or cpu).
FWIW - The slow conversion was probably from this - the machine doing the conversion worked about 1.5 days and complained it was out of memory - in reality it was that the cache directory in use filled the entire disk. Realizing that took a while (nervously almost had to reset the machine to factory defaults because it was unresponsive). To get the conversion going past that limitation I used an older USB disk that was lying around (probably USB 2) and empty, soft linked the cache out to it and let it run. I bet that slowed the process greatly - but I had no other option.
(I wasn't encouraged to fix this - what I saw of Lightroom wasn't exciting me enough.)