Go for a 770 4gig oc edition 390$ on amazon, and will anhilate your gpu card, while cheaper than the 780, and the pointless titan. the 290 falls into preference.
http://www.amazon.com/Gigabyte-GDDR5-4GB-WINDFORCE-Graphics-GV-N770OC-4GD/dp/B00CU9GOAO/ref=sr_1_2?s=electronics&ie=UTF8&qid=1390273632&sr=1-2&keywords=gtx+770
sell your card towards this.
Forget the 780, it's not worth the extra cost for small increment, as you would compare the small increment towards the titan gtx and the 780.
Common sense plays a important role too.
Sell your card on ebay, its safer and the safety features are good for new comers selling online.
1 Open a ebay account. (add your details and so forth) once logged in, upin the top right hand corner you'll find list your item "sell item" above.
2 open a paypal account, same way you did with your ebay account. once done, head back towards your ebay account and go to your financial details> link your paypal to your ebay account.
3 eventually you'll need to add your bank details, some buyers will ask how you will except payment. (if they say they'll pay with check, decline it, if they money order it to your pank, try to contact your bank on any new trasnfers)
But overall papal is much easier, as most buyers and sellers usually have funds stored in their paypal account.
Paypals similar to bitcoins, it stores data as money and transfers it to your wallet, while that's a entirely new topic
http://pages.ebay.com/help/sell/seller_account.html