There is a distinction with regard to performance to be made here, the UI component has no affect on sand-boxed applications, it can be as bad performing as it will, it won't slow down the applications running in the various sandboxes in the least. A basic set of Qt5 Libs is about 27MB admittedly much more than just using MFC which is about 7MB, but nowadays 20 mb is nothing 50 mb is still nothing, etc... If one compares memory usage the difference is not that big, but admittedly how do you reasonably compare two completely different frameworks, how about comparing two tools as identical as they can be yet using different UI frameworks. For example ProcessHacker (plain C, no C++, no MFC) vs. TaskExplorer (Qt5) booth tools use even the same Backend library only the fronted is different. PH uses on my system 54MB of RAM while TaskExplorer clocks in at 91MB right now. Looking at the source code PH (not counting libs) is 3,1MB in size TE (not counting libs) is only 1,4MB also TE has a lot of PH functionality which is located in plugins I did not took into account here. IMHO that is a more than worth it trade of, especially if you take into account that time is one thing you can't buy more of... Now about the CPU Usage, admittedly that's probably where Qt really shows its weakness in comparison to plain C, I don't have a good way to compare this, but in my experience when working with larger lists or tree views that have to be frequently updated Qt can easily ground to a hold and clog up one entire CPU core. When idling TE's UI thread takes up about 8% of one CPU core, that sounds much, but hold on, PH also is not that easy on the CPU it UI thread still needs around 5% of one CPU core. Total CPU usage on my laptop is TE 0.9% and PH 0.6%. Now it took me days of optimizations to get TE there but its there. So I think overall Qt5 is not that bloated, at least not with regards to what counts most.