[popcornmix]

I'll try doing some testing regarding video playback startup times on the weekend and report back.
Normally I stream from a wired SMB share (USB HDD connected to a router) but I will try local playback too.

I wouldn't expect USB speed to affect time to start playback of network content (but please test, would be interesting if there were a difference).

If you play content from the USB, then a fast one should start quicker.
I believe there is a small amount of seeking at start of playback(*), but it's mostly read in large blocks, so the suqential read speed is probably most important here.

(*) It's worth testing a good (indexed) format like mkv (or mp4 or avi), as well as a bad (non-indexed) format like ts (or m2ts or vob) as they may have different characteristics.