Granted, you did mention iOS work, which limits your choices, but there are several laptops there that absolutely can compete as desktop replacements, including one I've used:

Dell Precision M6600, Core i7-2820QM 2.3GHz,16GB (can take 32GB), graphics cards up to Nvidia Quadro 5010M 4GB, 1080p resolution display, SATA 3 SSDs