Hi that led are a little old fashioned...now the new generation of led are very brights...
I think that moreover of the led, depend very much of the optics that they use...normally 1 Cree R2 could to be equivalent to 10-20w of halogen bulb. With 1 seoul P7 or cree MC-E would to be equivalent to 30-40w.
To generate this figure you need to compare output in lumens. You can get this info from the manufacturers. Two items that both produce the same amount of lumens are equally bright. The human eye will not see small differences in lumens. Some considerations are that the LED will naturally produce a more directional light, so it is at a disadvantage if you need a sphere of illumination. The halogen will probably give you better color rendition, but the LED should use less power and produce less heat.