i used to fiddle with all teh settings on mine (exact same model as 6c has just bought, same a yours matt?) anyway i tried a few random settings which brings up endless variations
then i read the manual and through this site which showed me something i didn't know about the set-up
MIG Welding - The DIY Guide
the wire speed stays pretty much the same even when changing the amp setting.
i usually leave the wire speed around 5 to 5.5.
power settings, the 1/min i found to be too weak even for thin panels unless you slow the wire speed down but then the penetration was poor, it just seem to lay weld on rather than melt the steel.
the next power setting isn't 1/max like i expected, but 2/min confused: maybe that just confused me
anyway, that is the power setting i mainly used for welding panels like the sills and screen surround etc.
for heavier work like the floors and jacking points that had thicker steel i set it to 1/max and maybe increased the wire speed slightly, not higher than 6 though or the wire seems to bounce
only used the 2/max setting for the thicker bits like the jacking point sleeve bits themselves
one other thing i found with mine which may be the same on them all? i was getting through an alarming amount of gas, only set it to around 4.5 on the regulator, just enough to hear the gas coming out so i knew i wasn't using excessive amounts whilst welding. then once i went to use it after fitting a new bottle a couple of nights previously and it had only been used for a matter of minutes. the gas ran out within seconds
i then realised that despite turning the regulator down each time it must still be leaking. after that i unscrew the reg a few turns from the bottle when i've finished, the bottles last a lot longer then
hope some of that helps, i can't fault the welder for the price