So Paint Tool Sai has been recommended to me for the longest time, and I finally got a trial version of it. It does have an awful lot going for it. The brush work is possibly the best I've seen, and also borrows some of the wet media approaches and colour palettes from Painter (a program I'd love to use on a regular basis, but has a long-standing grudge against my Intuous 3).
So I decided to mix up trying my hand at this and copying a masterwork quite quickly, and with credit to Mr Caravaggio we have this
The colour palette was definitely a big boon for me; without having to click into anything to select colours I could bounce back and forth only once or twice using the inkdropper. This meant more vivid colour choices, and a quicker turnaround. I was also looking a lot at underpainting and the effect on the final form. Was definitely a very interesting exercise, and hopefully I'll bounce back into SAI much quicker with the knowledge that it accomodates some of my preferences so well.
The actual UI is a few versions from looking truly slick, but it definitely gets a painterly job done.