TBH, I will go for the Evo (or any cheap reliable brand / model SSD). If you have plenty of USB port, 2 (or even more )smaller SSD in RAID 0 will increase performance, but may be more expensive as well.
The SSD war just start, IMO, there is no need to go for something has 5+ years warranty. By that time, a multi TB SSD is the same cost as the low capacity model now. Just go for something as cheap as possible, use it until it die (should takes 10+ years to kill a 850 Evo), and then buy another one.
My 840 Evo was a well known problematic TLC SSD. I choose that because that's the cheapest 1T model by that time. And it's 2+ years now. The SSD still works well. And TBH, I don't care about it any more. If it die (I really can't see that at this moment), I will go to buy a 2T 850 Evo straight away.
I use my 840 Evo for Photoshop, FCPX (anything up to 4K 3 layer, around 10 special effects). The Evo can handle that well via a SATA 2 port. Yes, just SATA 2, I have a SATA 3 PCIe card, but TBH, can't feel anyn difference in real world. So I remove that and install another GPU which is much more useful in FCPX.
Anyway, all I want to point out is that no need to go for more expensive SSD if no specific reason. Just pick the cheapest one, and then you are good to go.
For small files read / write, the SSD can't even saturate the SATA 2 bandwidth, USB 3.0 sure is good enough. And basically any SATA convertor won't hold you back. However, for benchmark, which is about the max sequential read / write, that will be hugely affected by sub quality enclosure.
OWC produce good enclosure, but they are over price in general, because you pay much more for the very last bit of extra performance that almost can't be utilise in real world.
Another issue about using SSD via USB is lack of TRIM. So, to compensate this, you may consider only use 80% of the SSD, leave the remaining 20% never used AND never partitioned. So the OS can't see it, which means the SSD controller can use them as over provision. Otherwise, after you write the very 1st TB data into the SSD, the writing performance may be affected due to lack of TRIM (GC can't clear the cell because the controller don't know which cell is containing unless (deleted) data from the OS).