My prediction for XMA is for it to slightly improve upon DoFP numbers. Domestically, I think XMA will open to $100M three-day (versus $90.8M for DoFP) with similar legs for $260M DOM. Basically I think the goodwill from DoFP will be good for a bump, but that the marketing (and thus the plot theyve been selling) isnt as strong. Also, the absence of most of the original cast doesnt help.
Internationally, I think things are a little less rosy. DoFP was very well received so normally I would expect some international growth. However, a strong US dollar means relative deflation for international currencies; if XMA sells the same number of tickets as DoFP it should do around $435M overseas (compared to $514M for DoFP). I think it will beat this (because of China), finishing around $500M foreign. Added all together, my prediction is for Apocalypse to gross $760M WW, about in line with Days of Future Past.