@Frenchy - most of them are done in default size. That should be no problem and run fluently on any machine.
I get little brush lagging with brush size over 1500-2000 and blending on 100% on 3500x2000 canvas.
Anything else runs fluently until it crashes.
No lagging at all.
I am not a computer nerd knowing billions of things, but your system is not weak for sure. Your Graphic card should be faster than my quadro2000M on my laptop.
There, working in 2560x1600 can cause some performance lag. Switching off HQ and switching on for saving can save some performance. Blending as a brush option is also a culprit.
Anyway, Photoshop CC 2014 totally fails with mixerbrush, so what.
Those Adobe ants working like crazy to release a slower version on each upgrade
So in comparison verve is fast as hell. (O.K. CS5 - CC the mixer brush works fine for me. Hahaha - I only discovered this "mixer brush" because I wanted to paint with photoshop like in verve....or at least a little bit. Shame on me I didn't discover it before. Anyway, verve is so much better - Art Rage? didn't touch it since ages...painter? what's that..ahh there is a DVD lying around but phhh. It's old version 9 and no reason to update or me. Oh sorry. That was not your question

)
I tried to recreate last one in big 3300x2000 - with half success.
This could be printed in a reasonable size.

- abstract14BIG.jpg (202.92 KiB) Viewed 8875 times
Edit - One can crop now, to try better composition


- abstract14BIGCrop.jpg (245.2 KiB) Viewed 8871 times