There is no set answer for this in relation to a specific size - Google released some statistics a while ago and the average page size was 320kb, I remember reading. What I would say though is that you need to concentrate on load times, so make your page as small as possible whilst serving the content how you want it to be, so it loads quickly. Check how quickly you pages load using Google Webmaster Tools as an indicator - though remember this is taking an average from a sample of visits.

And here is a link to a YouMoz post that is very helpful in guiding you through optimizing your page speed - http://www.seomoz.org/blog/optimizing-page-speed-actionable-tips-for-seos-and-web-developers

Hope this helps.