With the overheads involved, AC1200 should get you connected at around 867Mbps. AC1200 Wireless cards/adapters are priced affordably too.
That's good enough to cover TM 800Mbps , 500Mbps and 300Mbps plans.

If there are other isps offering 1Gbps plan above, you need to find better routers or don't forget higher end wireless adapters/cards such as AC1900, AX3000 or better to attain such speeds.

AC1200 should be enough for now to cover upto 800Mbps wirelessly for ISP plans in Malaysia for time being.

What is the connected speed for your wireless client? You can look it up under connected Wi-Fi status of your OS.
If it's 867Mbps or so and you are still getting very slow speed on your local based speed tests it means your ISP is at fault.

AC1750 router is good but it's hard to find matching AC1750 wireless adapters out there. Even it there is, you'll be paying a very high price for them while they're rare.