I guess the perfomance and load of the datacentre is much more important than a distance to it. By example I have european client who has DEV enviroment on US Seatle datacentre and PROD environment of the same account is on EU Frankfurt datacenter and I'd say that environment on US datacenter is much more faster than EU. Also the permeance varies, I mean ut is also depends on customer, not only on datacenter as environments of different customers perform differently event on the same datacentre. Customization of course also impacts and matters but not so drastically.