Question - On what basis are you determining you are using 80mm/s ?
The setting in Slic3r's Speed tab (assuming you set them ALL to 80mm/s - which you shouldn't....)?
Or is it the Slider in Repetier?
Or have you run this through gcode-analyzer and determined the tool-path speeds and applied the Vector to it ?
Because its impossible to make a statement of 'I print at X-speedmm/s'.. as the 'print speed' changes depending on if its Interior perimeter, exterior perimeter, infill, top/bottom, first layer, bridge..
It also depends on tool-path length for that travel. At each transition of direction it will slow down to the 'x-y jerk' value (with caveats, too many to list here). It will then ramp back up to its relevant tool-path speed using the acceleration vectors in EEPROM.. It also depends on Direction - a movement in the Y direction alone will move faster than a Diagonal movement in the X/Y direction.. This is why often 0° offset rectilinear infill can be 4-5 times faster than hexagonal or even 45° offset rectilinear....
So in short - there really is no such thing as 'I print at X speed' - and if you actually average it all out its usually much slower than the numbers would infer due to complexity of movement screwing it all up.
Now - regarding printing with a .6mm nozzle in general - You are moving a crapload (I believe thats the scientific term
) more volume of plastic than a .2/.3/.4mm .. Elmoret or someone smarter than me can give you the math I'm sure. You can't just expect to move a substantially increased volume of plastic at a faster physical speed - but instead you move more plastic for the same given speed which means you need to overall extrude less. So you don't run it 'faster' in terms of linear speed - as you are already moving *more* plastic which is where the idea that you can print 'faster' with a .6mm nozzle comes from. Your axis dont move faster, but for each movement, you do move more plastic, requiring less *total* time... by exploiting techniques of printing 1x60mm perimeter which is faster than printing 2 x 40mm perimeters..etc etc
Then theres the whole other thing regarding the different back-pressure and its impact to flow-rate/speeds as a result in the change of nozzle size with a constant melt-zone... but that's beyond my ability to articulate.
To ensure quality prints on a Stock solidoodle (meaning the mechanics, not the hot end so much) you really shouldn't run the exterior perimeters over 55 - you can push it based on the particular shapes geometry but it's a loosing game above that. Internal perimeters, happily will go up to 80+ (even 100) without turning too ugly... Infill is usually best served at the same speed as interior. Bridges boil down to a magical combination of temperature and filament.. There is values that 'usually work' but the 'Best' speed/temp combo is fairly dynamic depending on filament etc.. And none of this needs to/should change based on Nozzle size beyond some minor tweakage knowing the cause-and-effect of that setting you tweak.
tl;dr - Theres no such thing as 'I print at X-speed' , and, you print 'faster' with bigger nozzles by virtue of moving more plastic, not physically increasing speed.