"I have a linksys wired router which is fine but on the slow side. 3 pc`s connected with ethernet 100mbs"
Slow in what respect? At the moment you have three or four computers connecting to the router at 100Mbps, with each enjoying the full 100Mbps available bandwidth. If you change to 300Mbps 802.11n hardware, in practice the speed may be about 200Mbps shared between all connections. That will be considerably slower for each computer than your present arrangement.
If you really want a faster network for data transfer between computers, upgrade your hardware (router and all network adapters) to Gigabit (1000Mbps) wired ethernet. You could connect just the remote Laptop by 300Mbps 802.11n WiFi, which wouldn't degrade the network performance of your wired PCs.