Do bear in mind that the infrared look is maximized when plants are full of chlorophyl - better in spring and early summer, better with deciduous plants than conifers, whose needles don't have as much chlorophyl and are denser, reflecting less light. The Ilford SFX has never had that strong an IR effect. I think for best results, you should try to find one of the Ilford SFX filters (I don't know if they still make them or not - it would be a good question for Simon Galley here).