I have an HP Split X2, which is a 13.3 inch Windows 8 Pro tablet/laptop. In tablet mode, I get about 6-7 hours of battery, and about 4-5 more when attached to the keyboard base in laptop mode. I have no problem with touch responsiveness at all. However, if a 15.5' screen isn't large enough for you, then that will not be enough for you. Have you looked at this 18.4 inch Asus Transformer?
http://www.amazon.com/ASUS-Transform...957142&sr=1-14 It looks like it's a Windows 8 tablet that has a base station that turns it into an all in one desktop. Oh...and it also runs Android Jellybean. If I could justify another computer to myself, I would get it just for the coolness factor
Shari