Ive not seen the weigh in myself but I reckon this all comes down to how hard Rios actually tried to make weight. If he genuinely tried and failed then he should be very weakened and Id give murray a decent chance of winning by late stoppage if he can take the early barrage.
If Rios didnt really try, knowing this is his last fight at the weight anyway then he'll be very strong and John will be in a world of hurt.