All of these are citing the theoretical maximum rate for the raw connection. You will NEVER see this for actual use, since some of this bandwidth is taken up with routing headers, encryption, etc. Also, for best performance your router needs to be set to use 40MHz channels (20MHz is default.)
I recently reviewed another brand of router (not a travel router) that supports the "2x2" transmission mode that can theoretically get up to 300Mbps on the 2.4GHz channel. The manufacturer supplied me with a data sheet saying that they measured 135Mbps on this band, and I am sure this was a "best case" number. For a travel router such as the DIR-505 that doesn't support the 2x2 mode, you're not going to see much over 75Mbps in the best conditions.