1) Have you done
apt-get update
apt-get dist-upgrade
(or "raspi-config" and select "update")
to get the newest (and fastest binaries) from those distros ? With the latest 3.6.11 kernel and optimised libs using the HW floating point and other hardware goodies, the RPi is way faster that when running the default, half-a-month old packages.
2) Have you tried overclocking ? The UK-made RPis with Samsung RAM have no issues running at 1Ghz (from the default of 700Mhz) and with RAM at 600Mhz (default 400Mhz). The Chinese ones with Hynix RAM work okay at 800-900Mhz with 450-500Mhz RAM speed.
"raspi-config" and choose the overclocking option. None of them will void your warranty (you can void it only if you edit config.txt by hand and use the higher voltages needed to reach 1.1Ghz or higher)
You can plop a RAM heatsink on top of the CPU but unless you run-it outside in the summer, it's not really required for overclocking.
3) For compiles, configure the memory-split so the GPU will get only 16Mb of RAM and give the rest to the ARM. You won't have 3D or HW Video decoding (X11 still works) but you will have lots of RAM for compiling.