hi sorry its been a while, the guide i used for the mtu is this one...... https://kb.netgear.com/19863/Ping-Test-to-determine-Optimal-MTU-Size-on-Router (i used www.bbc.co.uk instead of yahoo)
as for resetting the vr2800 theres 2 options, the auto setup which is done from the quick setup tab on the main menu, if you want to set it to access point (to work with another router aka the not so smarthub 2) then its advanced\operation mode then select wireless router mode, you will then need to go to advanced\network\lan settings and disable DHCP otherwise they will not play nice together.
As said previous im currently running a g.fast connection with a modem mtu of 1520 and the router is running 1492 (highest i can get it to go), im sure when running in vdsl mode it was set to 1482 or 3 and for me it worked fine, it is possible though my line is setup differently as i also had it connected via the annex a/l/m option and i had sra enabled (advanced\network\dsl settings) which according to the user guide is supposed to enable the modem to make adjustments on the fly in regards to line sync.
try following the guide first and see what you get
