Best open back headphones for under £300

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Dignified
Basically I wanted to improve my audio set up for my PC. I thought how better to do it than add some great headphones to the mix. I was looking at Sennheiser HD 650!

They will be driven by an Asus Xonar ONE DAC (USB) and paired with an audio technica AT2020,

If you can think of anything that beats this for the budget I am also open to suggestion! Thanks!
 
Solution
Any of the HD5xx or HD6xx headphones will be great. I have 3 different pairs of HD5xx plus a set of the noise cancelling for on airplanes.