Here's the deal.....

US still has a strangle lock on CLT - slightly broken now by Air Tran's service to BWI and ATL but that makes up about 1% of the airport's departures vs. 90% on US. When the deal with HP is done - fares will be rationalized. Until then there are very few flights where US can charge sky high fares and most of those flights are out of CLT or PIT and a few back-water non-EAS stations. So for the time being - either wait till the last minute and see if you can get an e-saver, pay for CLT or drive to GSO.

Never been to GSO but heard it's a good airport.

If you don't board at GSO your entire trip will be cancelled.

As irritating as it sounds - I would fly back to CLT rather than connecting through PHL. If DCA is an option that isn't bad but CLT will keep you on mainline jets for the longest time I believe.

Also, if you have someone drive you to GSO and don't have checked bags, you can fly out from GSO and get off in CLT throwing away your ticket to GSO. Done this several times - just don't inform the airline (though many people do it).

As for DL - I would hihgly suggest US - they have a better FF program - the ATL hub is ridiculous - flying times are longer with that routing - but most of all your chances of arrinvg on time are substantially better connecting in CLT or DCA over ATL.