.I have FIOS with gigabit speed
I think you really might have meant to say that the FIOS might have Gigabit Ethernet ports.
But, that does not tell you how it will perform as a router. I would expect the FIOS to be about the same, or less, as the AirPort Extreme that you have now, in terms of actual throughput.
If you check the Router Charts link that I provided, you will see that another Ubiquiti router.....which is about $350, and rated for Gigabit.....checked out at about the same speed as the AirPort Extreme. The Ubiquiti model that you mention above is about $100. It is possible.....but also unlikely.....that the $100 product will outperform the $350 model.
If you are considering the Ubiquiti that you mention, it might be a good idea to understand the store's return policy.....in case the router does not perform as well as you might hope.
Study the router charts, and choose one of the top 5-10 models if you are looking for speed.
Or, find other test reports from unbiased sources. Simply stated, in most cases you cannot trust the claims that are made by most manufacturers, because very few will even quote a throughput number.