The logic boards in the 867 and the 1ghz are the same board. The only difference is there are a few resistors on the board that set the CPU speed. If you are good at SMT soldering and have some spare resisitors (IIRC you need 1 or 2 extra resisitors to up the speed) you can swap/add the appropriate resistors and change the speed. With no problems of overheating.

You can even overclock the board. IIRC the board can get to 1100/1200mhz before it refuses to work. (Although you need to find alternate methods of keeping the board cool for that)

I remember finding this info back when I got my 1ghz. Unfortunately the site I found was long dead and only accessible via WayBack, and none of the images worked (which may make locating the correct resistor locations difficult).

EDIT: It seems I saved copies of the sites I found back when I was looking at overclocking. Going through my files I found a copy of http://www.macxtrem.com/articles.php?article=71 which looks like it may apply to the 867/1ghz model.