Hi. I have had good results using the Efke IR 820 film. I used the same Gossen meter as you have set to 4.5ASA. I originally bracketed one stop above and below 6ASA which meant that I got 12 shots to a roll. From this I concluded that 4.5ASA worked best. The camera used was a Nikon FE. The filter was the Hoya R72 and my general technique was to use incident readings. I would, however, recommend bracketing as others seem to use a lower speed for this film. I would also advise you to wait until there is plenty of sunshine as you are more likely to get usable negatives when there is plenty of IR around.