How Signal Integrity check in Altium Designer compares to HyperLynx?
For 1 and for HyperLynx, it can be pretty good. The main differences I have seen is over/undershoot isn't as bad as the tools predict. Also some vendor's IBIS models are better than others, taking into account packaging of the IC and providing monitoring at the die pad, rather than at the IC pin/ball.

For 2, there isn't much of a difference below 1 GHz. At higher speeds HyperLynx has an option that includes lossy transmission lines.