New warhead researched, must I design new missiles?

[martinuzz (OP)]

I've just finished researching 2-stage thermonuclear warhead.
Now, when I go into the missile tech creation screen, and choose a previously designed missile from the dropdown list, I see that the warhead strenght per MSP already has been filled in in the missile stats box.

Does ths mean, that my old design automatically uses the best missile tech, or do I need to design a new missile to make use of the new warhead?

[Andrew]

You need to design and build a mk2 missile

[sloanjh]

I've just finished researching 2-stage thermonuclear warhead.
Now, when I go into the missile tech creation screen, and choose a previously designed missile from the dropdown list, I see that the warhead strenght per MSP already has been filled in in the missile stats box.

Does ths mean, that my old design automatically uses the best missile tech, or do I need to design a new missile to make use of the new warhead?

To expand upon Andrew's answer, the thing you're looking at is NOT the parameters of the old design - it's what you would get with the new tech if you used exactly the same warhead/engines/fuel/etc. ratios as in the old design.  It's intended to help you remember what you did in the old design while designing the new one.

To see the performance of the old design, use the tech (ctrl-F7 IIRC) screen - the numbers should be the same.

John