With all respect to the responder in your other thread, he provided you with background information about the factors influencing your data transfer rates, but not yet with a specific solution of your current problem. But given his suggestion of a potentially restricting WiFi connection, there is a way to find out if your current WiFi speed is indeed a limiting factor, and that's exactly what Virtual1 suggests.
If just copying the required file to your Mac (to work with it there) is faster than than opening the remote copy over the network, it would seem that the latter approach adds 'overhead' (possibly caused by Excel) in addition to simply transferring file data. In that case, increasing your WiFi speed to 802.11n would not likely help you much, but you would have some idea of where the problem is located.
