As a matter of fact I JUST got home from being at the Monster 1200 training in Las Vegas where we got to do a 2-hour ride on it! The national launch of the Monster 1200 is coming up next Saturday April 5th, when it will debut in dealerships all over North America. I think in general most people would not be debating between a Monster and an 899, they are vastly different bikes with a completely different focus. One is a full-on sport bike and the other is a naked street bike. Monster is WAY more comfortable, versatile, easier to ride, lower seat height, etc. 899 is higher performance, sporty riding position with tall seat height, razor-sharp handling, etc. Despite specs saying the HP is nearly the same, the 899 revs up a lot quicker and has a more aggressive power delivery, and it's a lot lighter, it's a noticeably faster bike. There's a big difference between the race-tuned Superquadro engine in the 899 and the street-tuned Testastretta 11 Degree engine in the Monster.
One side note though, since you mentioned it, the Monster 1200 puts off a lot of heat from the engine, just like the 899 and pretty much every current liquid-cooled Ducati. When we were sitting at stop lights on our ride, I noticed the heat quite a bit, once you're moving it's irrelevant. So I would say heat would be no concern at all in picking one bike over the other, they both put off heat.
One side note though, since you mentioned it, the Monster 1200 puts off a lot of heat from the engine, just like the 899 and pretty much every current liquid-cooled Ducati. When we were sitting at stop lights on our ride, I noticed the heat quite a bit, once you're moving it's irrelevant. So I would say heat would be no concern at all in picking one bike over the other, they both put off heat.