Just try your hardest to save as much of the water as you can from the tank BEFORE you start tearing it apart. So you have the clean water. Then get your fish in buckets, vacuum your gravel to some extent and drain the water. Then take out the gravel, and do your thing. Put it all back in, gravel and remaining water, then fill the rest with water of equal Params. Ive moved a Large tank like this upstairs, and across town. The water they are in contains traces of life. Things like smells, pheremones and feel. This will help lower the stress on the fish reducing any "incidents"
I have also done the 100% method Many times, but if you are really wanting a true opinion, there it is.