All of those cards should run fine on your HX 520watt. See here is a list of the power draw of the video cards you listed, Keep in mind this is the power draw of a whole system with the video card:
So the HD 4890 is the most power hungry and that system needs 322watts max. The HX 520 watt has 500watts on its 12volt rail. Which basically means your power supply should be more than enough for any of those video cards. And your not even running an i7 processor, so your system will draw alot less power
But also If those video cards are in british pounds, than i would say your getting scammed. The core 216 you mentioned is $300 U.S right? And the HD 4890 is over 323$ U.S. These video cards are alot cheaper in the u.s ($170 for the core 216 and $250 for the HD 4890).
or am i converting this wrong?