Training the Wimmei would be a good idea, but be warned, they take a hell of a lot of work and you need to go to classes, dont try it alone with them, it wont work! I can put you in touch with some very good trainers who do HPR's

As for the lab, at 7 years you may want to think about another - with 18 months to train a new one, the time scale is about right. But there is no reason why your older lab cant continue to go out with you, maybe not all the time, but dont just stop taking her. As you have said, she acts as a mentor to the HPR and will do the same with whatever dog you get next.

As for taking a green dog on a formal shoot....I have seen "world class trained" dogs run riot whilst part/self trained ones behave!

At the end of the day, you have 2 dogs that are poles apart...Labs are easy to train, Weimeraners are a challange, but the results can be great. For rough shooting, the HPR is ideal although they dont like thick cover that much. We run a Lab (mine)a Weimmie (other halfs) and a Cocker (other half's - not that you'd know!)

Personally, I'm not 100% keen on HPR's, but its each to their own