In general the closer server will have the lower latency, which is a good thing but not a big thing.
The only benefit to lower latency is a lower risk of stale shares. It's not geographc proximity but topographic
(bandwidth, number of hops, congestion, etc) proximity that makes one server closer than another. The US server in CA
is much closer to NJ topographically than the EU server.
The issue with Nicehash is there are seperate order books for EU and US so they don't have the same orders
and don't pay the same to miners. The payout is the weighted average price of orders with active miners.
More miners pushes more work to lower priced orders and more orders pushes the price up. There is usually very little
difference between them but large changes in orders or miners can cause price volatility.
Order bots actually help reduce the price discrepency because they usually place similar orders on both boards.
I get more dropouts mining to USA then to Europe but not always.
I have used both and for me not much improvement with one over the other.
As for how it routes from NJ to CA (topographic path) I can tell you my ping times are about 75 to EUR AND 65 TO CA. WITH Eur having less drop outs. and as you said there are price differences.