One of my bosses has one of the pico pjs youre talking about, and they also have a full size optoma hd141x (under my recommendation - succeeded by the hd142x model now).
The pico is 720p and they say it is very dim unless in a dark room. The optoma is alot better to them since they wanted it to be in a more permanent setup for a home theater the longer they had it
Not that they didn't think the pico was good - it was a commodity that became a necessity to them
Just keep that in mind - once you get a projector you might want to always have one.
--
That said, if you don't expect the above to happen with you two - the 720p (or higher) variants will be pretty satisfactory for nighttime use