I'm working on a similar strategy as you.

Another card I would add to the mix is the Target Red Card -- which gives you a 5% discount off of Target purchases (it all gives you free shipping for all Target.com orders). I recently used this card to buy some third-party gift cards online, and when combined with a coupon was able to save 14.5% off the face value of the gift card.

Between DW and I, we currently hold and use:

• Amex Blue Cash Preferred -- 6% for groceries, 3% for gas
• Citi Forward -- 5% for dining, bookstores, movies and Amazon.com
• Sallie Mae Visa Signature -- 2% on all spending
• Chase Sapphire Preferred -- 2% for travel, dining and no foreign transaction fee (they also had a nice $500+ sign up bonus)
• Target Red Card -- 5% discount
• Amex Hilton HHonors -- 6 points/$1 for cable

I think I calcuated somewhere that I should hit around 3.75%-4.25% this year, excluding signup bonuses (which, together, DW and I have received about $2K in cash/statement credits, 30K SPG points, 60K Delta points and 100K Hilton points).

The only thing I'm missing is a 5% gas card, but at our spend it will net just $34/year in additional rewards compared to Amex BCP. For the cost of a hard inquiry and a new account, I'd rather get a card with a $300-$800 signup bonus and be covered for 8-1/2 to 23-1/2 years worth of additional gas cash back.