Did some more exploring tonight. Saw n77 on both my USM and Visible SIMs, but never for long enough to take a screenshot, let alone do a speedtest. VZW's coverage maps are *massively* overstated for n77, at least here. Had to go pretty far north to even get those glimpses. Finding T-Mobile n41 was miles easier.
Just figured out this is a waste of time. US Mobile and Verizon lock the eSim to the emei while T-Mobile only uses it to see that you have a capable phone, like Red Pocket does with physical sims (although RP does keep track of what phone you are using it on with the emei.) So @Trip was right in this case on liking physical sims.
Verizon has a reputation for being frugal with MVNOs. After looking around, I also decided US Mobile was my best option. People have gotten C band on it. Hoping for esim for my S21 Ultra. No luck so far. Red Pocket does not claim Verizon 5g, although they say Soon!(TM). I do see some 5g with it.
Typically MVNOs are deprioritized, thus I am reluctant to claim truly getting top speeds with one.
Did some exploring yesterday/last night and didn't find a shred of C-Band, including with my brand new US Mobile SIM. Did find 4CA CBRS but the site seemed backhaul constrained; both that plus 15x15 B2 and band-locked 2/66 got me 190 Mbps or so.