Is a ditching really a desparate enough situtation that you'd want to try the chute? Most ditchings in non-chute aircraft are survivable, even in low wing fixed gear planes...
Not sure that is the question.
The question I think is if you are going to ditch is the degree of injury on average likely to be moe or less with the chute?
I might add I dont know the answer.
Ditching into a six foot swell mind you is always going to be interesting.