I signed up to specifically answer this question.
I do game development with Unity3D and ran it on the Dell Venue 8. I ran a seen with about 500 draw calls (not an optimized scene), 5 1024x768 textures, and one directional light with real time shadows. I also ran a platforming project I'm working on. The first scene I mentioned ran in the editor at about 15 to 20 fps. This is actually not bad for editing and working on a project. The second project I mentioned ran smoother than that. I was able to be productive in Unity running on the Dell VP8; however, if you can, I would recommend holding out for a different baytrail tablet.
I actually have a blog post on this topic I'm releasing later tonight.
Seeing as how I just signed up out of excitement for this question, I haven't gone through the forum rules; so, I'm hesitant to post any links. If it's okay to post links, I'd be happy to send you in the direction of my website. You could also just google "step 2 digital production". Again, as of the time I'm posting this, my post about my Dell V8P experience won't be up for a few hours yet.
Update: I just put up my new post about my experience with the Dell Venue 8 Pro and Unity3D, plus other software. I didn't notice any rules about not posting blog links; so, here is my experience :
http://www.step2digital.com/2014/01/how-mobile-can-you-get-a-guide-to-art-productivity-with-windows-8-1-tablets/
Let me know if you have any additional questions. I'll try to answer them if I can.