Modern bloat comes from the software footprint, not so much about performance gains anymore. Compare the UI of MenuetOS with the latest GTK and the 100 shared libraries involved.
It's not so much that C would be slow but that with C and high-level languages it's very easy to do lots of the wrong kind of work.
C is so close to assembly that these seems quite unnecessary. Although I do agree with one of the developer's points that Assembly has a kind of beauty about it.
http://www.cconcepts.co.uk/products/publish.htm
Lol. Looking at those dialogs brings it back. I probably laid most of those suckers out.