In my opinion that film is more of a 100 or even 64 speed film anyway, you're better off having exposed it at 100. Don't underdevelop it to compensate. I've never understood why it's sold as a 200 speed film. If you want actual EI 200, Double X is a great choice.
It depends on how it's developed. With normal agitation schemes, the effective EI is about 1/2 box ASA (assuming your meter, shutters, thermometers, etc. are reasonably close). That's because the film doesn't sit in the developer long enough to fully develop the shadows.
OTOH, if you use an extended development/low agitation scheme - Semistand or EMA - you can get full box speed and still keep the highlights under control ... depending on developer and film combo, of course.
I base this on:
- Tons of actual densitometer tests with multiple films and multiple developers
- Looking at many, many negatives
- Seeing the results other people are getting
- Observing a recent misbegotten thread here on the difference between EI and ASA. It's a really exciting read ... no, really, it is.
In any case, it actually doesn't matter. What matters is what you have to do to get the results you want. Some magical EI or ASA or development incantation is kind of to the side of the point. The only way to figure this out is for people to try fiddling with this stuff themselves.
tl;dr Shadows take way longer to develop than highlights. Most "standard" development protocols are designed to keep highlights under control - by keeping the development time short and agitating frequently - and will not give you full shadow speed.