I personally find the 378s good for short distances - but easily get tired of standing up on them with the frequent stops. It is for this reason that when going from the FCC GN route to Stratford, instead of getting the Moorgate train to Highbury and Islington, I'll go all the way to Moorgate, hop on the Met line one stop (or whatever comes first - usually a Met, which is good as they're always empty!
) then straight back off at Liv St, rush across the concourse, find the next Stratford train that I can get to before it leaves (helpfully the boards at Liv St still show trains after the doors have closed and don't take them off the main concourse departure board early) and then jump on - no intermediate stops - to Stratford! Don't know if it's faster but for a medium length journey the 313/(I think it's 314s I get?) seats more comfy