Rollei IR-400(S) is going down in sensitivity over 750nm rapidly. So you need a 715nm or 720nm IR filter. Then you have to expose around iso 6-12 depending on the IR circumstances.
When using an IR760nm filter no bandwith is left for the film.
The Efke IR820 is a bit more sensitive over 750nm. But the regular speed of this film is iso 100 only. When using above filters you have iso 1,5-3 left. Maybe with a 760nm filter and iso 0,5 you can have reasonable results.