I am really wondering that so many Screen/UX-/UI-Designers are using Photoshop. I was and still am a lover of Fireworks CS6. Photoshop was and still is a Photoediting-Software and not a layout/design-application in my opinion.
And as I´m also doing frontend and prefer the method of designing in the browser directly cause responsive websites are just a thing no app existing can handle really well not to mention within a fast workflow / production-process.
I often get designs from 3rd party agencies which are >100MB PSD´s.
Open them in fireworks, save and then you have a 3–4 MB file (of course depending on the design and style — but flat ui & shapes in PS, don´t do that) which is superfast to handle. Guess Sketch would behave similar.
Also I have the guess that AI/PS CC 2015 is running slower on my macbook. Unfortunately one fact is that Apple has totally buggy drivers in Open CL & Open GL which would speed up rendering amazing. Also still Apple does not support 10-bit. Therefore it would be interesting how the speed is on windows. I´ll update my OS X 10.9.x to Windows 10 cause I also do a lot 3D & Motiongraphics and OS X (especially 10.10) is not longer an option for a fast workflow due to the bugs and missing essentials.
I´m also of the opinion that Adobe should charge lower for the whole CC or introduce more flexible packages like e.g. 2–3 base apps and 2 optional apps (monthly) where you can switch apps depending on your projects when you are e.g. needing after effects for a 1 month project and indesign the next month. They work on this I guess, so let´s see what the future brings.