I have a 13" tMBP which I think its great in case of screensize (often use it with an external screen), however I've been disappointed with the performance. I do both graphical design and coding. I've now got the opportunity to upgrade it with minimal costs beside the price-difference. I think the 13" is more than expensive enough as it is, but I suppose I'll be more happy to to spend a little more for something I dont feel lacking resources. Can I expect the quadcore + dedicated GPU to make a big difference for me (I'd buy the cheapest tMBO 15")? I do have the UltraFine 5K which works ok with the 13", but not fully fluid.