1. It seems stable now (80% tdp, +100 core, +600 ram), but it still slower than the other card (same brand, same model) by 20 H/s. Is this normal?
2. so card 0 accepted 31, card 1 accepted 40, card 2 accepted 30, card 3 accepted 14 & rejected 4 (this is the slowest card which was mentioned above). Why some card get more accepted than the other?
1. Yes its normal. Basically in order to get it stable you reduced the power to the core by 5%. This is turn lowered the hashrate.
Even though cards have the same model and SKU they can have variable hashrate. Im assuming AW is mining ZCL and or ZEC. For those you dont need to have memory so high (500 is good as suggest by phillip). Lowering your gpu temps and adding airflow might allow you to improve push this low hashrate card depending on how youve setup fan profile in afterburner etc.
2. Card 3 is unstable and has significantly higher rejects. After adjusting afterburner reset the counters and monitor for miner software.