I would recommend to focus on unlocking all permanent Common, Uncommon and Rare Req cards from Silver Packs and then focus on unlocking the Ultra Rare and Legendary permanent req cards from Gold packs. The main reason for this is that Silver Packs offers 2 permanent reqs for 5,000 RP while gold packs offers the same number of permanent reqs but for 10,000 RP. This gives that the expected amount of RP that you have to spend per permanent req from Silver and Gold Packs are the following.
While you open Silver Packs, the best indicator for when you should start to open Gold Packs is to open Silver Packs until the permanent req cards are replaced with 1,500 RP (this card: picture
). If this is done, you will need to spend approximately 25% less req points compared to if you opened the Gold Packs first.
Finally, another tip is to sell all none permanent reqs except for RP Boosts and Weapons/Vehicles/Powerups that you enjoy to use in order to reduce the expected amount of time you need to play in matchmaking in order to obtain enough RP to unlock a new permanent req.