Alienware 13 & U processors
For GW2 you want a M or HQ CPU and not a U. The lower clock rate will make that much of a difference. And Broadwell is performing less then an i5-4200U, but with MUCH longer battery life.
http://www.digitaltrends.com/computing/intel-core-m-5y70-broadwell-tested-benchmarked/
If your looking at an i7-4510U, you are better off buying the i5-4200u to save on cost, as the performance between the two are going to be minimal for gaming. They are both lowly clocked and have only 2 cores. And the i7 has minimal value-add above an i5 for the current costs (259~ for the CPU upgrade on Dells customization page).
Desktop: 4790k@4.6ghz-1.25v, AMD 295×2, 32GB 1866CL10 RAM, 850Evo 500GB SSD
Laptop: M6600 – 2720QM, AMD HD6970M, 32GB 1600CL9 RAM, Arc100 480GB SSD
Laptop: M6600 – 2720QM, AMD HD6970M, 32GB 1600CL9 RAM, Arc100 480GB SSD