My favorite custom brushes for blending are the square canvas brushes (1 through 5) under the artistic preset. I've gotten incredibly smooth blending with them. One secret for me, also, is that as I'm blending I frequently reselect color in the area I'm blending as I'm applying new strokes. I have one of my pen buttons set to the "alt" key (windows) to do this. Experiment with where and when you select the new color from what you put down and you'll get a feel for blending them.
Edit: When I use these, I go for very smooth blending. Not sure they would give you oil brush strokes or how they would play with your intent. I look forward to what you put out once you sort out your style in ArtRage (hint: you better show us
)