Re-entry Speed of ICBMs/SLBMs and Other Factoids

I recently read an article on the old Titan II missile, which begged many questions.

According to the article, the Titan II reaches an apogee of about 500 miles and a maximum velocity of about 15,000 mph. The article suggested its velocity during the atmospheric boost phase is relatively slow, but didn’t say how slow.

At about what velocity do so-called “high-speed ICBMs” (not sure if the Titan II qualifies as high-speed) narrow down on their targets? I can’t imagine any missile being able to sustain 15,000 mph once it has re-entered the atmosphere. In general terms, how do ICBMs overcome the considerable thermal stresses associated with high-speed flight in the atmosphere?

Also, how are the MIRVed warheads deployed–and at about what altitude? Does each warhead have a propulsion unit and guidance system?

Note to mods: This information is public domain, I think.

No rocket scientists?