I am currently working on a bigger project and have got multiple pages and art boards and the performance is just terrible. Could be that I am on MBPwRD, but I really doubt that. Gonna get a thunderbolt display and see.
Also there are many glitches with exporting that have not been yet fixed and I have even got an email from the Sketch developers saying that they did not notice the bugs I reported repetitively.
That said, I kind of regret getting rid of Photoshop and working in Sketch and Pixelmator full-time. I may be putting Photoshop back on as it so far renders everything as it is - that means perfectly and can export it that way as well; but I am going to put PS back on only when the CC version gets "a better trial" - I am not willing to pay around 70 bucks a month and not fully own the app for as long as I want. That's way too much for a subscription like that. Also my be cause I hate subscription system, don't believe cloud and I want to own the product. Not having problem like this with Sketch - I even purchased a copy for my fiancée - 50 bucks is a steal, I would not hesitate to drop 300 bucks, if they would fix bugs, performance issues and added all the features I need.
Can't wait what bjango is going to come up with, Marc is an awesome designer, the Skala is gonna be a blast.