This thread has reminded me that I have some 35mm IR film in my fridge salad draw. I'm waiting for some constant sunshine here in the UK before using it... It might be a while...
I love the tones in your images, but I actually prefer the ISO 12 images, but then I do prefer darker prints and the others could be printed that way.
As for exposure, when I've used it in the past with my Pentax MZ5N 35mm camera, I exposed with the IR filter on the lens used and bracketed the exposures over 2f's in 1/2f stop increments. Surprisingly the cameras meter did really well and I got a good set of negatives.
But on both film and digital exposures, I never used the IR red line on the lens, but used a middle f-stop of about f8 to be on the safe side. The red line was only slightly different than the 'normal' focus mark on the lenses anyway.
Terry S
UK