Interesting, didn't know the compiler converts to C++, yes, then if you just switch away from GCC (to clang or msvc) it may be as fast as C++ itself (depending on how good this converter is, ofc)
About the video from dave's garage, it's okay-ish, but not enough, I use this site as a good reference, they are old timers, and have a lot of benchmarks from mandelbrot to reverse complement. As you can see: C, C++ and Rust are the fastest on an average of all their cases (note that unfortunately they don't use a LLVM for C and C++ which could make them even faster).
For games I do recommend C++, it's not only blazing fast but also the best in terms of content and tools produced for game development, but to be honest you can make a very good and efficient game on any language.
Java. for instance, I have a history with it and oh boy it's a painfully annoying language, specially for game dev, but still it was minecraft's first development language, it all comes to how you make it, as long as you leave the heavy lifting to the GPU you can even make hardcore games in python (that may be too much lol, Lua maybe?)
So yes, if you're comfortable with QB64, go ahead I and finish it up in there, I know it will be just fine