I download all the portable version from 0.8.19 to 0.8.23 and I think that something happened between the calibre-0.8.21 and the calibre-0.8.22.
On the 21st I'm able to convert the CBR to PDF in 39 seconds, on the 22nd the conversion simply hung (starts 6-8 parallel processes that use a huge quantity of memory but no CPU).
For now I will keep the version 21