if i may say, plugging in the KT150 into an existing amp using the kt88 does not give you extra power, only extra heat....
but for new designs where operating points are different and transformers may be bigger, then by all means go ahead...
the thing i dislike about these newer tubes is the lack of design operating points on the datasheets,
unlike in the old mullard KT88 or even american RCA 6550, where the tube manufacturer gives a complete set of operating points
where builders can easily apply in their tube amp builds...