Check your DCR with all of those cams. I think you will find the XE cams may put you over 8.5, particularly the XE-268. My 383 is the same as yours except my head chamber is 68cc, and I could not run the XE-274 and chose the Magnum 280 instead. DCR is 8.46 with the 280 Magnum, which is okay with 92 octane. Anything over 8.5 and you risk detonation on pump gas. I think that is why CompCams recommended the larger cam with more overlap in order to bleed off some compression.