Morning Bryn - I'll be honest and state that Im not the most clued up on TTFB as its something that I recently started playing with.
Based on my tests though the results are subjective to where you are testing from and the OS / http server thats running on the server.
TTFB is important despite there being contradictory statements about it saying that its not important.
Our 700 ms is high, and possibly due to the fact that we have php hosted on IIS and for this reason we're busy with a deployment of our sites to new servers running centos with litespeed.
We're using openlightspeed on our new directadmin server and our own testing has shown very low ttfb results, including page speed when compared to other providers.
For our test we took a clients website and copied it onto the new DA server and with the aid of wp litespeed plugin were able to improve the site speed dramatically.
You and others are more than welcome to order a free account and do some testing on our servers if you are interested.
Below are the details for the 2 month free trial
Order any DirectAdmin hosting package at the url below and ensure that you use the promocode DEWE39AW8R at checkout to qualify for 100% discount for two billing cycles, billed per month.
Please ensure that when you order, that you select monthly billing
https://client.absolutehosting.co.za/cart.php?gid=40
The coupon code is valid as per below
Monhtly billing, for two months
Valid from 14/08/2019 - 14/10/2019
Discount applies to upgrades - downgrades must be requested by ticket
If you do not wish to continued with the services at the end of the two month period, ensure that you cancel the services via the client service area ahead of the second renewal date.