BASC has a good leaflet on the subject
https://basc.org.uk/wp-content/plugins/download-monitor/download.php?id=723
"There are two types of steel shot cartridges: Standard Steel and High Performance Steel (See table below for criteria). Standard Steel cartridges can be fired through any gun proved to the standard level (ie most “Nitro” proved guns, proved to at least 930 bar)
and through any choke. High Performance Steel cartridges should always be marked as such on the box and should only be fired through guns that have passed Steel Shot proof. These guns should be proved to at least 1320 bar, be stamped with "Steel Shot" and a have a Fleur de Lys proof mark to prove it). Most High Performance steel can be fired through any choke, but it is recommended not to use choke greater than a half for shot sizes BB (4.1mm) or larger."
In standard steel you can use any choke according to CIP (except on very light weight game Guns).
In HP steel you can use any choke up to 4.0mm shot size, however a fixed choke gun choked more than 1/2 would need to be opened up to pass the steel proof test as the bigger shot size could be used.
Regards the striking power you are limited in shot size, load weight and momentum, I stand to be corrected but I have yet to see a CIP HP clay load, only the bigger load weight or shot size game loads.
Momentum is velocity (in m/s) at 2.5 m from the muzzle multiplied by load weight (in kg). The limit for standard steel is 12 Ns.
Black gold steel for instance is 28g 7.5 shot ,1450 velocity (marketing) 400 velocity (mps v1 used to to work out momentum) gives a momentum of 11.2 Ns which is below 12 and therefore standard steel. I doubt you would need more than that for clays.
For game loads if you up the load weight you obviously have to drop the velocity and the limit on shot size could be a problem for some quarry.
Like I said if you are shooting clays no problem, with hunting your cartridge choice is more limited but there is still plenty out there in standard steel.
Edit to add:
the gamebore website is worth a look as you can see a graph and work out the difference between their shells.