I'm curious too because I've opened the exact same cards and you have + 1

Feb 10: Delta SkyMiles AmEx
June 15: Chase Continental
June 25: Citi AA Visa + AmEx (this is when I really started reading the forums and became obsessed with the idea of churning - I wish I'd known more earlier!)

Some people on here say that Chase is more likely to approve you if it's been a month since your last application - 6 months is even better, but there's lots of anecdotal evidence of people saying they've been approved for multiple Chase cards within the same week, etc. So I'm not sure there's anyway to know if you'll get the Sapphire until you try for it... and if you get turned down, you can always call their reconsideration line. They seem to be really generous in approving you if you call them.

I'm trying to prioritize between a Citi AA Visa Business card (75k), which I could apply for at the end of Aug, or the AmEx Premiere Gold (hopefully 75k if they bump the bonus), the Chase Sapphire (50k), or ALL of the above on the same day. I don't have a sense of whether that would be too much or not.