To reply to your question about comparing cracks in the two areas:
Both areas have some really good quality crack routes. I love the hand-size lines in the Dacks as well as the off-width, whereas J-Tree, the finger cracks are just exceptional.
I find J-Tree cracks tend to be sharper with more crystals. For strenuous cracks in both areas, I always tape, but especially in J-Tree. More obscure routes in J-Tree tend to be *very* grainy and coarse -- e.g., Junk Clump, Sheepbugger's Wall. I find that taping is especially important if I'm pushing my grade -- I'll slip a bit from being such a weak bumblie and I'd rather tear tape than skin.
Both the Dacks and J-Tree tend to have many features on the edge of the cracks or on the face around the cracks (with exceptions, of course). Cracks in these areas are not "pure" like at Indian Creek.
Both areas have cracks of all sizes -- from off-width to hands to fingers.
As a general rule, I find crack climbing in J-Tree to be cleaner -- i.e., not as dirty, mossy, lichen covered, or brushy. -- as the Dacks. Obscure crack routes in the Dacks are, well, gardens of dispair (e.g., Cobble Hill, Echo Cliff).
In both areas, the cracks are generally not uniform, meaning that you don't need 7 of the same piece. I find that doubles from #00 TCU through #3 Camalot (or as big as you want) is usually sufficient. (Of course, you sort through and carry only what you need for a given route, leaving most of the stuff at the base.) Both areas eat up nuts of all sizes, from RPs through, say, #8 or #9. In the Dacks, a double set of RPs is required for some routes; in J-Tree, I've never needed that many.