You won't get any support from Intel here since replacing the WiFi card that is not in the OEM list of approved WiFi cards. Also, you must show proof of OEM approval to be able to replace the card yourself. Read more here: Intel� Wi-Fi Products — Regulatory information regarding hardware installation or upgrade
The behavior that you're experiencing is not normal or maybe due to your laptop hardware incapable of handling the 7260AC properly. I have an Intel Dual Band Wireless-N 7260 OEM on my laptop and I do get that 180 Mbps throughput on a 300 Mbit connection.