I use quite a bit of SFX200 behind a cheap IR720 filter on the front of my Mamiya RB 67 lenses. The results are quite nice but the infrared effect is rather mild. Effective speed with the IR720 filter is EI = 6 for sunny day landscapes and about half that on overcast days or in the shade. Images have visible grain at 8x10 or larger and I think that reflects the origin of the film which is supposed to be Ilford HP5+ loaded up with IR sensitising dye.