I went through this only a few weeks ago. Have you seen my thread, including the flash meter calculations, on the last page? In the end, film-plane needed to read less than f/0.7 measured at ISO 100 for a 400 film. Since my meter could not measure flash less than f/1.0 I had to get it to that level, then reduce further using flash power adjustment.
Watch out for uniformity of flash output at the film surface, and check the repeatability of your flash. Finally, bear in mind the comments about suitability of a flash sensitometry exposure vs. your expected target lighting scenario.