The 250’s a good pretty recent card. If you’re being offered that rig for a real good price it might be worth giving it a go before making a workstation card purchase but there’s definitely supposed to be a pretty considerable difference, especially with programs like you mentioned.
I’m sorry this site isn’t any help in Britain but as a reference this card looks like a good fit for some heavy lifting for your purposes if you decide the 250 won’t cut it.