I find Double-X to be a tad on the grainy side but very nice tones. I too find it develops very dense negatives when shooting at 250 and developing according to the massive dev chart, so I switched to metering it at 400 to compensate a bit. I haven't tried it with a bunch of different developers but that's definitely on my list when I get some time.
I submitted a suggestion to Kodak on their cinema website that they sell it online in 100' rolls and pointed out that ORWO is doing this already. Never heard back, and haven't seen it show up in 100' rolls yet. I sold off some of my excess Double-X a while back and even after trying to compensate for my costs of materials to get it into 100' bags and cans (thus making it far more expensive per foot than just ordering a 400' can from Kodak) I ran out of spare film long before I ran out of people willing to buy it from me. I think Kodak should definitely reconsider not offering it in 100' rolls. Those could be used by both filmmakers (in Eyemo cameras, etc.) and still photographers.
Here are the links to the ORWO products (one slower, one faster than the official ISO of Double-X)
Interestingly they are currently sold out of both of those in 100' lengths. Sounds like a market with some demand, to me!