No disrespect but I think you will be struggling to get 250+ (I'm assuming we are talking sterling here) for your card. The average on Ebay over the last couple of weeks has been around the £200 mark (EG.
http://www.ebay.co.uk/itm/1809517904...84.m1423.l2649) and out of this you have to take P&P (assuming you can keep your parcel under 2kg, then even this is almost £10 for Next day delivery) and then there's 10% auction fees. So the realistic return is more like £170 cash in hand.
The reason why I know this, is that I've just sold one for a quick cash sale at £150! Though first to admit I wanted a quick sale and was doing a forum friend a favour (not this forum). Slightly lower than I wanted but concerned that a price war on current gen graphics cards is starting to break out and could not be bothered with selling on Ebay. Especially since they now hold your payments for 21 days for consumer electonics!
Unluckily there's nothing that drops in price faster than previous generation top tier graphics cards.
Good luck though if you do decide to sell

You may be able to find someone to part with more cash that maybe doesn't know better.
PS. There are loads coming up on Ebay at silly money but they then don't usually sell. One's with £200+ starting prices, are not even getting bids on them. Though there's always the chance that a couple of bidders will go mad trying to out bid each other.