What difference would a MTHFR test do except leave you with less $ to use to continue to tweak and test supplements, meds etc. You already know to try methylation related supplements. The results of teh test won't change your strategy and may not be so relevant if you have a heavy metal component.
HMs foul up Methionine Synthase which has its effect on the methylation cycle very close to where MTHFR has its effects.