Do I even need an external SSD for editing with 4 TB internal? Purchasing i9 Macbook Pro this week.

This is a previous post from another member but I have the Exact same question! Would really appreciate any help.

' I'm looking at the new Mac Book Pro with the i9 processor (with the Radeon Pro graphics options that will be available later this month). I'm trying to decide how much internal HD space I want. You can go up to 8TB, but it costs thousands of dollars more to do that.

I've always edited on a desktop with an external RAID drive (recently an SSD RAID). I edit multiple streams of 4K footage and have had no problems doing that on my Mac Pro.

This was posted previously and I have the same question...can someone please give their thoughts?

"I've always heard it is better to have your OS and FCPX on the internal Macintosh HD and your FCPX project on an external drive. However, given the new MB Pro's optional 4TB internal SSD drive space, I'm wondering if it would be a bad idea to edit video on the MB Pro with everything (OS, FCPX and the project) on the internal SSD drives?

Are those internal drives fast enough that everything could be on them and I'd still get really great performance? Or would I still be much better off getting an external Thunderbolt 3 SSD and editing with my project on it?"

Any advice would be greatly appreciated.