Dell is currently offering 12% off for Black Friday and Quidco is doing 7.7% on any dell purchase. Not sure if these can be used together or if Dell will decline the cashback but if they don't decline you can get:
* 17 R4 with a 1070, 256GB PCI-e / 7200 HDD, 16 GB 2667mhz Ram and QHD G-Sync for £1,867 inc
* 17 R4 with 1070, 7200 HDD, 8GB 2400mhz RAM and QHD G-sync for £1,623 inc
So you're effectively looking at a differential of £243 for an upgrade which includes 256GB PCI-e SSD and 8GB more ram.
Priced separately you could pick up a Samsung 960 256GB and Samsung 16GB Ram for about £200 so potentially save £43. Not great but you know, every little help