It depends on alot of conditions; type of protocol within TCP, MSS, TCP_DELAY ( nagle), the type of server process, your SRTT, window-size, etc....
TCP is only as fast as the returned ACKs. So having a bigger or more importantly; a faster return path, can help with the overall TCP transfer speeds.
the problem is ; " your last mile is just on part of he picture"
Also network links are changing every secs with load%, the thing same with the routers, servers and switches,etc..... So can' t say or expect the same performance for ALL traffic every time.
just my 3 cts due to inflation

Now if you want to see how important link speeds are, build a lab, and set up a asymmertical link in size, and squeeze your return path and monitor your thruput. This would give you an ideal of how bandwidth effects your delivery.