Ive shot the Speer 45 300gr Unicore softpoint in both MMP 3P EZ and Crushribs in my 50 Extreme with 100gr or more of BH209. It prefers MORE.

Maybe mine is a bit tight but both worked within reason. I liked the 45LC 250gr GoldDot Defense bullet better mainly because with just 100gr it shot very well and expands great at low velocity.
BTW the Nosler Partition 45 300gr has about the best SD/BC in its class and are on sale at Wideners for only $23 for 50. Both the 260 and 300 shoot good in my Extreme. The 300gr doesnt come alive until about 105-110grs. Even the Partition 44 250 and 45 260 have fairly good SD and BC.
Im still waiting for a good source of the new DeepCurls in 3 calibers to be available. They are just renamed GoldDot Hunting bullets. Using longer 45cal bullets i use smaller OD sabots and with shorter/lighter bullets i use a bit tighter. My first time out with a new gun, i take MMP "shorts", MMP 3P EZ and black Crushribs.
The Extreme 50 is kind of a powder hog so be prepared to load them a bit warm sometimes to tighten up the groups. Some groups really tighten up at around 110grs of BH209 or T7 equivalent.
I never tried the Red CRs but im guessing they will be very tight in a Knight Extreme 50 and a .452 bullet, maybe a .450 would be ok if you could find any. Those mic out to about .507 and mine is tight enough with a .504 loaded sabot.