Anyone who pushes the limits of a machine needs tuning options. If you can't turn knobs you have to keep rewriting code until you happen to get the same effect.
At least with code hacking around the GC's behavior that code ends up being portable across the ecosystem.
There doesn't seem to really be a good option here either way. This amount of tuning-by-brute-force (either by knobs or by code re-writes) seems to just be the cost of using a GC.