The difference between any providers of various servers, from professional servers for forex traders in the location. As a rule, professional servers are located in data centers processing financial information, in London it is Equinix: LD3/4
Usual web servers are located somewhere nearby. So pings will be higher anyway.
I am aware the difference can be a few milliseconds.
But even with the 20ms at home I get excellent results on a demo account.
With a real-account a VPS and latency of 1.9ms, I get slippage higher than specified by the broker.
So what I think is important is where my order is located in the queue
Which brings me to the question: What has the most negative impact on the quality of trade-execution (slippage).
Is it:
a) the extra delay even if it's in an order of a few milliseconds because the VPS is in another datacenter.
b) the number of routers between the VPS and the trade-server. (data-package congestion)
c) Lot of traders using the same algorithm wanting to trade at exactly the same tick (instantly exhausting the available liquidity).
d) a secret data-package priority agreement between broker and professional clients. (if it exist)