Hey, thanks for all the help guys. I have a 25a red, but may wait until I can get the R72. Since it will be a once in a blue moon thing, I'll just get a cheapie off of Ebay rather than a Hoya. If I meter at ISO 12 without filter then add filter, what ISO do I tell the lab personnel that it was shot at??
Ilford SFX is a 200 ISO film. It will give normal results when exposed without a filter under normal results and developed to a "standard" contrast.
With any film, when you communicate with a lab about shooting speed, you are actually not talking about film speed at all.
You are talking about what contrast you want them to develop the film to.
So if you want them to increase the contrast of the film, you ask them to "push" the development.
If you want them to decrease the contrast of the film, you ask them to "pull" the development.
If you want the film to be developed to a standard contrast, you ask them for standard development.
With other films, it is often helpful to increase contrast if one is forced to under-expose the film. So that is why people tend to associate "push" development with situations where the shots were metered at an EI higher than the "box" or ISO of the film. Pushing doesn't really add sensitivity to the film, but it does make underexposed film look marginally better.
In my relatively limited experience with near IR films like SFX I've found that standard developing is most likely to work best, so that is what I would instruct your lab.
The advice included here and elsewhere about the special metering one needs to do with near-IR films and filters like an R72 are essentially methods to deal with the fact that the filter blocks so much light, and the fact that our meters actually don't measure the near-IR light itself (just the visible light that accompanies it). The meter readings give us the ability to make a somewhat educated guess, but bracketing is still a good idea.
None of the manipulations involving the Exposure Index you are using for metering really affect the development.