There are multiple tiers of missile (and ballistic missile defense).

Especially with ballistic missiles, the longer the range, the faster the inbound warhead will be in the terminal phase (roughly). So longer range ~= faster meaning more difficult to intercept.

"Iron Dome" is the name generally used to describe Israel's lowest tier set of defenses. Very roughly Iron Dome is designed to defend against stuff that you could plausibly fire from the back of a truck, and have a max range of around ~50km.

Very roughly, these were intended to take on something like GMLRS (realistically, massed volleys of unguided rockets) - these are rockets that one or two people could conceivably manhandle, and are traveling in the neighborhood of Mach 2-3. One of the key innovations of Iron Dome is its ability to quickly ascertain and design on which rockets were unlikely to strike valuable areas, and only engage the actually threatening ones.

The next tier up is David's Sling, and then Israel's wider set of high performance anti-ballistic missile systems. Returning the the range <-> speed thing, we'd need something like a medium range ballistic missile to get from Iran to Israel. For something like the Shahab-3, that's like ~Mach 7 during re-entry.

If we step up to IRBMs (so something that China might use to strike at Guam), we're probably talking like Mach 10.

Interesting stuff, thanks for the long and detailed response.