Pings to 1984.is:
From Palo Alto : round-trip min/avg/max/stddev = 183.514/184.035/184.898/0.466 ms
From Amsterdam : round-trip min/avg/max = 36/37/39 ms
From London : round-trip min/avg/max = 48/48/50 ms
Obviously this can vary quite a bit depending on what peering you have at your disposal.
For reference, from Palo Alto to London:
round-trip min/avg/max/stddev = 156.236/156.921/158.271/0.834 ms
For latency, I would choose NY/NJ or similar if you really want one location to serve both EU and US; Though this isn't ideal, it does lower the latency to West Coast US quite a bit.
From San Jose to Newark :
min/avg/max/stddev = 73.462/73.547/73.660/0.078 ms
From London to Newark :
min/avg/max/stddev = 72.836/74.323/75.600/1.200 ms