Good question! How do you size the HA2 links? I haven't seen any documentation on this, but I ran into this video on YouTube -> https://www.youtube.com/watch?v=4hFQypgOAGk. Go to 1:15:47.
If my math is correct, the PA-3250 supports 63,700 connections per second which requires 122 Mbps over Ethernet. In this table, I would populate the IP and UDP headers if used. The Bytes per Connection is the total of the indented rows. The Total Bits per Second = row1*row2*row7.
Connections per Second 63,700
Bytes per Connection 238
Session Sync Bytes 220
Ethernet Header/FCS 18
IP header (20) 0
UDP Header (8) 0
Bits per Byte 8
Total Bits per Second 121,284,800
So, GE or higher is plenty, assuming the bytes per connection in the video is correct.