That's exactly what I'm doing because I'm still within the first year of my AMEX Gold PR. Once the annual fee comes up on that card, I'm canceling it, but until then, I'm using it for gas and groceries and getting 2x points. Everything else got put on my SPG (until I met my 15k spend threshold), now everything is going on my BA Visa (until I get to the 30k spend threshold on that), then it'll move back to SPG. And when I stay at Hiltons, I use my AMEX HHonors to get the 6 points/dollar.

It's all about playing the game of which card is best to use for each purchase.