@muvideo,
I have not seen different microbolometers for differing temperature ranges. The normal approach to enabling higher temperature measurement is for the insertion of attenuators and wavelength filters in the optical path to control the thermal energy reaching the microbolometers surface.
The PM695 has options for a 1500C and 2500C. These are filters/attenuators fitted indside the camera on a moving filter holder.
Obviously when a camera has different temperature measurement ranges it will need to have appropriate calibration tables for each. When I select a different range on my PM series, the camera immediately carries out a comlete recalibration routine, not just NUC.
I am not aware of the maximum temperature that the E4 microbolometer can cope with but the Exx appears to be capable of over 600C, and I do not think it needs an attenuator or filter to achieve this.
Modern microbolometers are stated as being "Sun Safe", meaning that they cannot be damaged by being aimed at the Sun (much of the energy is 'out of the lens bandpass'). It would be hard to overload such a sensor to the point of damage, unless you were very determined to do so and directed in-band energy at the sensor at very high levels causing overheating of the pixels and eventual oxidation or melting of such. In the domestic environment or even the workshop I would not expect such conditions to exist.
Flame filters for live furnace inspections are explianed in this FLIR document:
http://www.flir.com/cs/emea/en/view/?id=41800High temperature filters are not cheap to buy though .... take a look here:
http://www.netzerotools.com/testo-885-2-infrared-camera-high-temp-filterUS$1619