You cannot plug both the High wall mining implant and the Foreman mind link at the same time
Upgrades for the riches - Heard of the new mining upgrades CCP first released that were so unbalanced that a Rokh out-mined a Hulk? They cost Maple Story Mesos a fortune; people spent millions, and then, silently, were nerfed and did not work.
A patch was brought, and their bonuses were changed... those who know what I am talking about might still be crying about it... thank the Gods (hello BSG!) I didn't fall for them. They finally ended up like this...
Mining Foreman V however is valid, since you can just form a squadron with an alt and you both will receive the bonus, even if you are in a Hulk or a barge.
The mining implants do stack, however as you may have guessed, you cannot plug both the High wall mining implant and the Foreman mind link at the same time.
Name CPU Penalty Mining Amount Bonus Price
Aoede 7.50% 9% 500-600mil
MLU II 12.50% 9% 20-25mil
Carpo 8.00% 8% 200mil
Elara 8.50% 7% 30-75mil
Erin 6.00% 6% 15mil-200mil
MLU I 10.00% 5% 50K
Just so you know, you can fit two MLU II on a Hulk ... yes, you will need Mining Upgrades IV whereas the other only require Mining Upgrades I, but you will save quite a bit of ISK!
Do not forget about the Gypsy' KMB-# implant which add CPU to your ship... you can now fit 2x MLU on a coveter with it!