Havoline 20-50 is also car oil, there is no seprate 4T in 20-50 category by havoline. Thats y zic 20-50 would not make a negative effect but its added minerals will make positive one.
People who r claiming that they use low visocity 10w oil in winter and than switch back to 20-50 in summer will surely suffer. No oil company will suggest u take this step. i have seen many company representative stopping people from this type of practise. U will suffer in long run and engine wear tear will be done at fast pace. Thats simple logic, no rocket sceince theory. U can jump from low to high visocity oil, but not vice versa