There seems to be too many variables here to come up with a solid answer. Like has been mentioned, there is really no way to come up with an "apples to apples" comparison.
Like this......... which of the following is safer.
1) An NDL full penetration (with no exit other than the entry) cave dive in fresh water where the water temp is 70F, their is 50 ft of vis, no current, and the cave has been totally mapped and previously dived by many others.
2) An NDL full penetration (with no exit other than the entry) wreck dive in open ocean water where the water temp is 70F, their is 50 ft of vis, co current, and the wreck has been totally mapped and previously dived by many others.
Like this......... which of the following is safer.
1) An NDL full penetration (with no exit other than the entry) cave dive in fresh water where the water temp is 70F, their is 50 ft of vis, no current, and the cave has been totally mapped and previously dived by many others.
2) An NDL full penetration (with no exit other than the entry) wreck dive in open ocean water where the water temp is 70F, their is 50 ft of vis, co current, and the wreck has been totally mapped and previously dived by many others.