If not heat-sunk properly high-output LEDs can get very hot, which can greatly reduce their operating life. IIRC, they also are less efficient at high temperatures. The data sheet for the LED should have thermal info for that device.
The voltage across a single white LED is 2.7V up to about 3.5V, so if you're running at 1 amp that's 2.7 to 3.5 watts it has to dissipate. The high voltage (compared to a silicon small-signal diode's .4-.7V) is due to the fact that the LED is made from a much different semiconductor. Voltages higher than about 3.5V indicate the package has more than one series-connected diode inside. I found some that require 50V to operate so, yeah, lots of diodes inside those!
There are ways to get Digikey and Mouser to help you find parts you need. Part lists displayed by Digikey and Mouser can be sorted on any displayed parameter, so if you click on the column header for "light output" or similar you can see the brightest ones right away. It also is helpful to tell their search engine to only display active components so you're not looking at obsolete parts.
You also can filter on the package type, light color etc. so you can more easily find parts to meet your requirements. If you click on entries in the parameters listing (the very top of the page), the search engine will display how many parts meet that parameter value. Helpful if you find they have zero or very few devices that do.