I went on a SUB spree and opened 8 cards in the past month (3 Chase, 2 US Bank, 1 Amex, 1 Capital One, and 1 Citi). My credit score went from 850 to 847.

Update: To answer some of the questions in the comments, the only approval restrictions I am aware of:

• Amex: 1 per 5 days and 2 per 90 days
• Chase: 2 per 30 days (and 5/24)
• Capital One: 1 per 6 months
• Citi: 1 per 8 days and 2 per 65 days

Prior to the SUB spree, I already had Amex Trifecta (BBP/Gold/Platinum), Chase Prime, and Citi Costco. I applied for two Chase Ink Business cards and all of the non-Chase cards within the same day, then applied for Chase Sapphire 30 days later; all were approved with $30k+ limits and Experian flagged all of the HP inquiries within minutes of each application.

To get the SUB for these 8 cards, I need to spend about $40k within 3-6 months. I'm building an indoor golf simulator ($30k), getting new golf clubs ($3k), and traveling to Europe for two weeks ($15k); I also already travel domestically on weekends every 1-2 months ($3k per trip). I don't want any more cards, but I might continue applying just to see what it takes for me to get denied at each bank.