TL;DR: Use Qt or .NET, both frameworks will do the job for you! Personally, I recommend Qt over .NET, but that's based on my opinion.
You ask about performance and whether or not the frameworks you mentioned are capable to run your appliciation, so I want to give you some examples:
- Qt (afaik not quick) is used by: Autodesk Maya, Modo, Nuke, Houdini ...
- .NET/WPF is used by: Autodesk 3ds Max ...
- Custom developed frameworks are used by: Unreal Engine1 (Slate UI Framework, see below), Unity (unitygui API, see below)2, Blender (based on OpenGL)3 ...
If you are interested in game development, you might have heard most names I mentioned. All of those programs are huge and complex applications. So yes, any of these approaches can be used to build "large growing application".
As a result, I can't recommended you a framework over another (except for my personal preferences for Qt). Any framework should be able to do the job for you.
As I mentioned, the developers of Unity as well as Epic Games and the Blender Foundation have developed their own frameworks. Unity uses "unitygui" and provides a public API. You may learn it from there official Tutorial.
The Unreal Engine Editor is based on Slate UI Framework, which also public accessable and documented in the Unreal Documentation.
Blender is build using OpenGL and is Open Source.
Summary and general recommendation:
You should start with something like Qt or .NET/WPF, there are many books, online resources and communities to help you. If you are familiar with C++, Object-oriented Programming and something like MVC, this shouldn't be that hard.
If you want to use C++ and/or want to develop cross-plattform, go for Qt! .NET/WPF is not cross platform and personally, I would use it only with C#.
1 Unreal Engine Documentation
2 what gui toolkit does the editor use?
3 What is the framework using in blender gui?