Correct, Ta4HfC5 can withstand up to 4263K with tantalum carbide and hafnium carbide having temps of 4150K and 4201K respectively. However a material was invented in 2015 that based on computer models would handle up to 4400K being made from hafnium, carbon and nitrogen (HfNC).
Of course they haven’t actually synthesized it yet, 
As for uses it’s main use in real life appears to be control rods as it absorbs neutrons quite readily. It can also be used in high heat thermocouples.
Hafnium oxide seems to be quite useful in electronics as a replacement for silicon oxide in some applications.
I’m also thinking as it’s so similar to zirconium, it might be able to be used as an alternative for it in some applications.