I don't have any comparison data, and the only beer i've done this with is only 2 weeks into aging, so please keep that in mind when preparing to flame me.
I utilize an oak dowel for both flavor and oxygen, because as i understand you can get both effects from it. Regarding toasting your own:
Size - if you're going for flavor, going bigger isn't necessarily better. In the same respect a smaller cask gives MORE contact area, a larger diameter dowel will not significantly increase the contact area or oak flavor. Get a dowel to match the hole in your stopper. For mine, i chose 1/2" oak dowel from Home Depot ($2).
Toasting - check out this pic for temps/flavors.

I followed this to choose which temp to toast at. I've done multiple dowels at various temps, but have only utilized one for aging currently, so i can't comment on the impact various temps actually DO have on the flavor.
I took my dowel, fit it to my aging carboy by figuring what length i need, then cut to the appropirate length. Wrap the entire thing in aluminum foil and put it in the oven for four hours at the desired temp. Once out, take a torch or flame and char the surface of the wood for a couple minutes (though to me this seems optional). Once cool, soak the dowel in water for a couple days to take the wood-flavored edge off. Some don't do this, but it seems to me that if i'm going to let a beer age for a year in contact with the wood, i don't want harsh flavors from day one. Clean, insert in stopper, then use.