It sounds to me like you are right on the edge of choice/select, but still OK for YG.
Feed them for two more weeks next year would be my advice. Don't change anything until you do that, you might screw up your good thing.
If you do need to change, just be careful. You are at 50% British/Continental, so that is good. For my money, I'd try one of the SimAngus or SimRedAngus bulls out there, to keep you close to where you already are, but not move you too far and screw up what you've got. Look for above average marbling, but lower backfat, and a bigger ribeye. They are fairly easy toi find due to the nature of the cross.
Big point is that you are close, don't let somebody fool you into buying something you don't need, which is an extreme bull. You don't need extreme marbling at this point to move you, you only need a little more, not a lot more.
mtnman