You've identified the considerations you need to take into account. Ideally, 7:1 is correct as a rough rule of thumb (though up to 10:1 in real storm conditions!), but not if you'll run aground, or into other boats by doing so.
Then I suggest you need to consider the alternatives: can you anchor in a shallower area? Can you find an area more protected from wind/waves where 5:1 might be acceptable? Can you locate a bit further from other boats? Can you use a kellet, and a shorter rode to achieve the same effect? And of course, using proper anchoring technique is critical, and then testing that the anchor is holding properly.
Finding the right combination of these factors, without compromising safety is what's needed. Or maybe a new anchorage?
I usually try to anchor in 20 - 30 feet of water; anything more means alot of hard work hauling the anchor/chain up through a distance that my arm muscles tell me is much to large. If you have a windlass, that's different...