Way above my pay grade, but I will chime in with my 2 cents before we get the actual expert responses.
If you have 6-7# northern strain LMB, then I think you have done very well and I would consider those "trophy" fish. You didn't state the size of the 250 F1 LMB you stocked in 2020. However, they are still relatively young fish. Personally, I would wait and see if you can get some much larger LMB from that stocking.
I predict that your lake record for a LMB is going to keep increasing, and that the record will probably get shattered after someone catches a big momma F1 in a few more years.
If all of that fails, only then would I shake up your good existing fishery with gizzard shad if you are still in pursuit of trophy LMB.
Good luck in your pursuit of monster LMB! That particular pursuit must be contagious, because I know lots of people that desire that same goal. (Just imagine how many people Lusk knows in that category!)
