Does the Solar System Collisions system give accurate results?
http://janus.astro.umd.edu/astro/impact.html
It seems to calculate an impact energy, and then, based on the target, chooses the category of the impact to give you an idea of the results of the collision.
It’s accurate in the sense that I didn’t notice any glaring errors after poking around a bit. But it’s not doing a simulation or anything–it’s just a toy.
After playing with that calculator for a while last year, I did some digging on the correlation between meteor size and crater size and it turned out that the precise chemical and physical composition of the impact site has a lot to do with the size of the bang, and the size of the hole.