NMEA sentences; other GNSS

[Paul Theodoropoulos]

Two quickie questions, as I've read an assortment of conflicting things on 
our old friend the Internet:

1. What are the minimum/desireable NMEA sentences for a GPS receiver to 
send gpsd for timeservice? This page has a splendid summary of some of the 
NMEA sentences - http://aprs.gids.nl/nmea/ . I presume the following are 
required:

$GPGGA
$GPGLL
$GPGSA
$GPGSV
$GPTRF (? maybe?)
$GPZDA

2. On the ublox neo-M8T, it supports GNSS:

GPS
SBAS
Galileo
BeiDou
IMES
QZSS
GLONASS

I know that IMES and QZSS are specific to Japan, so definitely not needed 
- I'm in the U.S..

Is there any value in having anything other than just GPS enabled, for a 
stationary timeserver? Does SBAS help at all?

-- 
Paul Theodoropoulos
www.anastrophe.com