Weaves have maximum effects regardless of power. The fact they both capped out about 3 stories says to me that it is probably about the best you can achieve. Egewene like you showed stated that it seemed to be the limit no matter how she strained, and she wasnt strained to get them that far.

I think nyn lifting both at the same time would be more power then lifting them seperatly. Like when women link they dont combine their power, it isnt as efficient as that.