Jits on the desktop are usually bad not just because they do take more
memory but also because you need the build system of mono installed
which means more bloat.
Considering that Gtk# applications consume less memory than PyGtk
applications am puzzled by this blank statement.
Am not quite sure what you mean by "the build system of Mono", there is
no such thing as "the build system of mono". Maybe you mean that you
need to have the "mono" command installed?
Every compacting GC automatically doubles memory use - you have two
managed heaps ergo twice the RAM required. If you copy MS and go for a
three generation one then you risk trebling memory use over using a
non-compacting one.
The extra memory used for a compacting collector is in the nurseries. A
compacting GC can allocate memory during the compacting phase for
temporary objects, and release it back to the OS when its done.
So certainly during a collection you would notice more memory usage, but
it would go back to the used memory after the collection is over.