Currently I have a rMBP late 2013 with 16GB RAM, 512GB SSD 2.3GHz Quad-core Intel i7 and a 4k UHD ASUS 'retina' monitor. I'm thinking on getting the 5k iMac 4.0Ghz Quad Core i7, 16GB RAM, and 256 SSD plus 4GB video. Can anybody tell me if I'll notice a big difference in speed or screen improvement? color accuracy will be better than the ASUS but I'm already at 3840 x2160 and it looks pretty good. What about speed? I'm debating on spending $3000 for almost no improvement on speed or screen.