New Primary Router vs Access Point?

Hey, I have the new Asus RT-AC68R and I am currently setting it up as a wireless access point for my network, it's LAN to LAN with my Actiontec MI424WR router, I was wondering if there is a downside to using it as an access point vs a primary router?

Also, my laptop is only getting 72.2 MBPS on wireless when the advertised speeds are 150 MBPS, my network card is an Atheros AR9285

Thanks in advanced.