If you know how to use it, IMHO Painter's painting and natural brush and media capabilities
paint circles around Photoshop - regardless of version. Operative qualifier: "If you know how to use it."
Among the challenges of Painter:
* It's got a pretty steep learning curve
* Learning resources (books, web tutorials) are extremely skimpy compared to Photoshop (but I've heard very good things about the offerings via
www.EclecticAcademy.com)
* In order to get what I would consider decent results from it, one should have a fair amount of traditional skills in the areas of sketching, shapes, shadows, etc. (I don't) or be prepared to (or have a desire to) learn them.
Since you've got Painter Classic (Painter 5), I'd say install it and give it a go. Functionally P5 and P8 have a lot of similarities, so if you can get your arms around Classic, see its potential and want more, then I'd look into P8.
Don't be misled by "the upgrade price" promo. When Painter 8 came out that price was offered by Corel to anyone with pulse and a competing product, one of which is Photoshop.
Note: If you do get P8, beware there's a patch for it that literally needs to be installed
immediately after P8 installation (without having opened P8).
Good luck and happy painting...
~Danny~