I've read that the Lite6 fan is optional, and also that it is mandatory. I print with PETG only, at 245, and was thinking that if the fan really is optional then taking it off could give more time for the heat to melt the filament and thus allow higher speeds. Would this be correct?
You want to minimize the melt zone otherwise the filament will expand and bind inside the heatbreak/heatsink. It might be possible to use it without a fan but I'd suggest using a fan to make life easier.
Several places including here: http://www.filastruder.com/products/lite6 Not looking for super speed, just ease of use with PETG which needs higher ABS temps.
It is optional for some materials, but not others. I'll get that clarified on the Filastruder site. It is required for PLA, for example. PETG is a bit of an unknown.