Once your memory usage climbs and your OS starts paging/swapping things to disk, seemingly trivial operations that page in new code will take forever.
Linux desktop toolkits and dev environment utterly sucks. You'll have to develop 3 different codebases for Win, Mac and Linux. Worse still, you'll have to reinvent app updates technology if you go with Qt or will be tied into a different updating technology and still have to deal with piracy problems.
Or you could go with web-apps:
-> Easy to develop code
-> Can't be pirated
-> In built model of regular payments
-> One codebase for all platforms
It's not even a close fight.