If you are looking to push yourself, you’ve picked the right trail. I could see it being highly rewarding if you are looking for that type of challenge. I don't know exactly where you are from, but you should also check out the Great Range Traverse in the Adirondacks and the Pemi Loop in the White Mountains as well if you haven't already.
People who enjoy pushing themselves to the limit do those two loops in a single 24 hour period, whereas normal backpackers like myself do them over several days. I've never heard of the Devils Path being day hiked. It might be cause it's just too sketchy to hike in the night by headlamp.
Some quick stats on these hikes:
The Devils Path (Catskills) - 24.3 miles, roughly 9,000' cumulative gain
The Great Range Traverse (Adirondacks) - route dependent, the most common route is 19.3 miles and 9,137' cumulative gain
The Pemi Loop (White Mountains) - 33.4 miles, 9,051' cumulative elevation gain
The Pemi Loop and the Great Range Traverse are ranked #2 and #3 respectively in Backpacker Magazine's list of America's Harderst Day Hikes.
LINK - Backpacker Magazine - America's Hardest Day Hikes
For some reason, the Devils Path is not ranked, but that just might be that it's too difficult to be done in a day. I would never be able to average more than 1mph over any reasonable distance on the DP, but then again, I'm not a particularly fast or strong hiker.
I've been on all 3 and in my experience the Devils Path is the hardest terrain, followed by the GRT, and then by the Pemi. As far as scenery is concerned, I'd have to say that the GRT and Pemi blow the Devils Path out of the water. I did the Pemi over the course of 4 days 2 weeks ago which you can check out
here and a partial, failed attempt at the GRT
here. I have some day hiking reports on here that go across parts of the Devils Path too that I can dig up for you if interested.
Best of luck. Let us know how it goes.