I would reuse the Cooler Master Seidon and save the £90.
The Phanteks Enthoo Pro M is a nicer case for the same/less money imo. Just get a 140mm fan for the front.
Also the Gigabyte i5 660K/Z170X-SLI bundle is cheaper. There is also a slightly cheaper non SLI bundle.
My basket at Overclockers UK:
- 1 x Phanteks Enthoo Pro M Midi Tower Case with Window - Black= £59.99
- 1 x Phanteks Enthoo Pro M Window Edition - Black Full Acrylic Side Window= £69.95
- 1 x Gigabyte Z170XP-SLI - Intel Core i5 6600K Bundle **£20 Saving**= £304.98
Total: £449.62
(includes shipping: £14.70)
I did offer my cooler, he said thanks but no thanks. Did not want used bits, which is fine.
That Phanteks case does look nice. I will show the lad it. he may have already ordered.
cheers..

He really likes the mobo and other stuff.