The problem is most probably software specific. I am running OSX 10.9.2 on a rMBP with 16gb or Ram, half a TB of free storage and a 2.6 i7 and typing in pages lags a lot! I was on the phone with apple support UK for over an hour yesterday and they did not have a solution for me but at least they are looking into it. The program was not sucking too much memory and the rest of the computer was running smoothly. The only problem was with typing in pages. The length of the document didn't seem to have a correlation, as opening a new document and filling it with dummy text of up to 3000 words did not cause it to lag, but rather the amount of time I've spent on a document. The technician asked me to disconnect pages from icloud as he thought it could be connected with the constant updating, but this didn't help either. We've tried creating a new user account, testing the document in safe boot, completely removing pages from the system and then reinstalling, removing any plug ins like Endnote's plugin etc but NOTHING helped. And the weird thing is that: it's only typing that's lagging, scrolling, adding graphics, copy pasting and ANY other function would work smoothly... unless you tried to type. Also, the exact same document would have no problem being edited in pages for icloud.
I am surprised as to why there aren't any more people facing this problem allready.
I will keep this post updated with any news from Apple Support.