PS are known to stunt and reproduce at a lower rate than BG so you may not need LMB on the same stocking level as normally suggested. In your northern location LMB become sexually mature at a slower rate (often 2 yrs old). Also consider SMB and WE as possible adult additions. Even the experts (fishery science grads) who try the all-female LMB approach don't have long term success sexing LMB. Usually by year 3 LMB reproduction has occurred.