To be honest either of those will be perfectly fine as far as I can tell. For the Office applications and Sage there wouldn`t be any issues. I do all of that on a laptop that cost £100 less than you propose to spend and nowhere near the power of an i3 processor.
The one thing on your list that might concern me is the watching of DVD's. Two things you should check on the proposed laptops - Battery Life and the quality / volume of the sound. If the "claimed" battery life is less than 3.5 hours I would reasonably assume, based on experience that you couldn't watch a 2.5 hour DVD on it using just the battery. (DVD Playback seems to drain batteries very quickly and having the laptop plugged in would be sensible.)
Speaker quality is very difficult to judge but be warned that on some laptops at this price range they can be poor quality - "Tinny", no decent bass and poor volume. The only way to tell is to get a demonstration. And here is your problem. Lenovo are not readily available at the likes of PC World, Curry's et al.
Lenovo bought out the IBM brand and are a very well constructed machine. I would check out some of the reviews on this site.