I have all 5 on DVD, but Dirty Harry is the first 4K release I've bought. It's a fantastic remaster and looks pristine, reviewrs are saying its one of the best looking in recent years. There is no chance the VHS looks how it did when it was released. The tape will be worn and faded after all these years.
The new 4K transfer is taken from a scan of the original 35mm film and cleaned up and colour corrected, won't get any better than that. Same for the new sound mixes.
New 4K trailer
https://youtu.be/S6bnGiyBXuU