Hi Tricia,
I was on regular met and spiro last year - with major GI problems! I ended up switching over to XR - that helped. If you're right and the spiro lessens side affects, well then I'm VERY glad I was on it; I can't imagine what my side affects would have been without it!

Interesting theory though; I'd like to see what others have to say about it.
As for dosage vs. IR levels - hmm. I'm a little more than slightly IR and I'm on the highest dose for the XR (2000mg). Originally, my doctor was only going to leave me on 1500mg, but since AF was still a little off, she upped me to the 2000mg dose. She mentioned another reason too that I can't seem to remember right now. Whatever her reasoning, it worked great for me; I'm finally regulated!
Good luck. Hope the side affects abate soon.