Determining the frequency IGBTs can run at?

Hello.
I'm trying to figure out how to select IGBTs, and am wondering what to believe.

Here are two half-bridge modules:
CM400DU-12F, https://www.digikey.com/product-search/en?vendor=0&keywords=cm400du-12f
APTGT300A60G, https://www.digikey.com/product-detail/en/APTGT300A60G/APTGT300A60G-ND/1920592

According to the datasheets, the second one outperforms the first by almost every parameter i can see, twice or more times.
Only exception is the max current, which is slightly less.
Turn-on and off times are twice as low, gate capacitance is 4 times less, saturation voltage is less, etc.

However, it's datasheet says it is only good up to 20KHz.
On the other hand, the first (supposedly inferior) one is ran at 50KHz in this popular project with no problems - https://www.instructables.com/id/30-kVA-Induction-Heater

So, what limits the frequency in the second one?
Is it just marketing understatement of some sort in the datasheet?
Or maybe the first is ran outside of it's capabilities?

AFAIK, the delay times and how fast you can charge the gates are all that matters, no?

The 20 kHz rating is for regular hard switching applications with rated IGBT current. The induction heater application uses higher frequency but only a fraction of rated current and in addition a resonant load which can at least partly achieve ZCS operation..

high voltage switching devices adopt minority carrier devices to achieve high rating operation voltages, while it's at the expense of switching speed. The first one's need of more time to charging up the gate maybe not the sole reason.

'IGBT's do NOT have intricate body diodes, like mosfets do. However, manufactures often do you a favor, and put a high speed high voltage diode in with the IGBT package, for ease of use. Be sure to check how fast the diode is when using the IGBT with high frequencies. But, there are exceptions, some IGBT's don't have diodes in them at all, and may require you to add one outside of the package. You need to put the anode of the diode (pick an ultrafast high amp 1000-1200 volt diode) to the emitter of the IGBT. This will allow voltages to freewheel if needed, preventing your IGBT from blowing up.'
Details here is a brief text http://m.instructables.com/id/Semi-Conducting-A-Guide/step18/IGBT/

yep, what FvM said.