The f-stop XL Pro ICU actually is not a good fit for the Storm IM2500. Between the intrusion of the wheels and the 7" depth of the ICU, you'll have trouble closing the lid (the depth of the case, minus the lid portion, is listed at 5.2" on the Pelican website). I found this out the hard way - i.e., by trial and error - which necessitated shipping a bunch of stuff back to the dealer. If you like the dimensions of the 2500 case and want to incorporate the f-stop ICU, I'd take the previous advice and contact a Phase One dealer to source the ICU that is designed for this case. f-stop used to sell a shallower ICU but I don't see this on their website anymore.
The XL Pro ICU fits with room to spare in the IM2620, which was my eventual solution. I added about an inch of padding underneath the ICU to prevent the inner case from knocking around too much. The extra space around sides of the ICU allows the ICU to bow out a bit to accommodate oversize gear, and there's enough room above to stuff odds and ends in a lid organizer. Or you can order the case with the foam lid liner to keep everthing snug. However this case is a bit of a beast and exceeds current U.S. airline carry-on luggage size limits.
- John