For simple reference, cheap SD cards will have speeds around 75-100MB/s a gen 3 NVME SSD(What’s in the deck) Will have speeds around 2500-3500MB/s. (I should mention here that there are very substantial diminishing returns for many many games once you get beyond around 600MB/s speeds and you will not likely see a 3-5x faster load time in most games.)
High end SD cards can reach around 170-180+MB/s Which is about as fast as a pretty fast Spinning Hard drive, but with lower latency(Which is the biggest killer of HDDs, seeking to get the needed data).
Game load times will definitely be worse off of an SD card(Especially cheaper slow ones)
I picked a Samsung Pro 512GB SD card for my deck with claimed 180MB/s speeds. I’ve installed games onto it and even played Nioh 2 off of it. Load times weren’t terrrible, but could be faster. An inconvienence, but a cheap and easy way to double my decks storage and put lesser used games on the SD card.
You can also migrate a game from card to SSD or back easily.
Shouldn’t any dock that works via USB PD work for this as long as the lighter USB adapter is rated for enough juice?