I don't know. The only difference I can think of is when judgement happens.

Jesus spoke more about hell than anyone else in Scripture.

Judgement is eternal in this case also.

I agree that judgement is more immediate in the Old Testament but even then God relents much of the time. God is slow to anger but abounding in steadfast love (Exodus 34:6-7). I'm reading 2 Kings and the amount of times God relents to judge a wicked king shows how rare it is when He does.

I'd warn you against creating a dichotomy between God's character in Old and New Testaments. They are the same and Jesus Christ is the same yesterday, today and forever (Hebrews 13:8). The prophet Malachi also teaches this about God in the Old Testament (Malachi 3:6).

Distinguishing between God's character is the beginning of a trajectory that leads us to a false view of God.