I've just done a speedtest on JL and it came out at:
Ping 934 ms
Download 1.67 Mbps
Upload 0.00 Mbps <== this doesn't seem right but I can believe the download speed. Still much faster than the A380 OnAir on SQ, although about the same speed as their 777/A350.
I am rather hopeful that BA's speed will be pretty good.