http://www.cree.com/products/pdf/XLampXP-G.pdf is a direct link to the data sheet of one of the best generally available high power LEDs. It generates between 100 and 130 lumens at 350 mA@3V, depending on the chosen color temperature and the efficiency bin. That is about the maximum efficiency and it is a 1W LED there. That's about 5-6 times more light per watt than a typical incandescent bulb.
It can be driven without damage to at least 1000mA@3.3V and then will generate about 2.5x as many lumens at that drive current. All assuming you can keep it cooled to 25 C. At 100 C you lose about 15% efficiency. These are indeed not easy to cool. And an array of them with a substrate, the drivers for them and the optics would not exactly make for an inexpensive modeling lamp. The CRI is between 70 and 80. Another drawback compared to incandescent for some uses.
Ronald