Thanks for doing that John, it's very interesting: It looks like 150 at C24 is pretty much comparable to 195 at C16 in terms of deflection: I didn't think the difference between the two would be anywhere near as much, from the other information I've seen. Of course, the C24 may be more expensive even in the smaller size (I'll have to get a quote) but if it's not too much more, the extra 2" might be a useful space saving: It would certainly reduce the step up onto this floor from the new access door, which might make it more user friendly.
(It took me a while to get back - I've been away for a few days and it seems Firefox can't connect to the server from other networks)
All the best