I would not do it and would be real concerned with what you are doing now. Two different brand tires on the same axle with different patterns (and different type rubber gripping coefficients) means different handling conditions between the car and the road for each tire on the same axle. Perhaps safe at 20mph or maybe even 40mph. BUT at 60mph or 80 mph with slight moisture on the roadway--this may prove to be very dangerous and cause the car to become uncontrollable. I have concerns with different tires on different axles, but never different tires (brands) on the same axle. Safety to me is most important and handling under emergency conditions (or bad weather) is key to me.
PS--Based on your wording, I am wondering what you mean by 60% tire left. Is that just eying it? Have you measured the exact depth of the treads? Even though legally some States allow no less than 3/32, that is considered borderline dangerous by many. Federal law does not allow trucks to have front tires less than 4/32. I consider it time to change tires at 5/32 in order to have good road grip and responsiveness to steering. So--what is the lowest tread depth on each tire.