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I'm far from being an expert, but I have some experience fiddling with settings for PETG. It tends to be slightly stringy and slightly blobby compared to PLA, because it's so sticky. I've been printing a lot in PETG recently (making face visors for you-know what!) and have used several different brands (Enotepad, Steadytech, Real, RepRapWorld, Fiberlogy, Ooznest). Unlike cmoelege's experience, these all seem to print at their best, with least stringing, between 240ºC to 250ºC (as indicated by my printer!). I run my heated bed at 70ºC and use a borosilicate glass build plate with Elmers disappearing purple glue stick (the white also works, but you can't easily see where you've put it!)

Since 250ºC (and the slight temperature overrun on heating!) is above the melting temperature of the PTFE in the Anycubic heat-break tube, I've converted my hotend to all metal. I've also swapped to using a 0.5mm nozzle as my standard size and have had no nozzle blockages since changing about 9 months ago! I have had one blockage, but this was a piece of plastic detritus from the extruder hob jammed down the side of the filament in the bowden tube and nothing to do with the nozzle!

Optimising print speed and retraction is essential. I also have an Anycubic Kossel Linear Plus but I've swapped out the original extruder for a (genuine) E3D Titan, which I have fitted half way down a leg/tower with a close tolerance Bowden tube (i.e. 1.9mm internal diameter) that's 50cm long. I use PrusaSlic3r and, for PETG, my retraction distance is 4.75mm at 125mm/s (deretract speed also 125mm/s), wipe while retracting, 25% wipe before retract, with a Z-hop of 1.5mm.

For determining print speed, I use the Maximum Volumetric Flow function (MVF), because PrusSlic3r caps the linear speed automatically based on this (and I would hope other slicers do this too). It's importance is that MVF is the maximum rate at which your hotend can adequately melt the plastic filament to produce good prints (It depends on a few factors specific to each printer design, but I think all filament manufacturers should publish an MVF guide figure for each of their filaments, perhaps one based on an E3D V6 (because it's a very commonly used or cloned setup (& the Anycubic V5 J-type hotend is very similar in performance) and another for a high melt-rate set up like the Volcano). You cannot print faster than the MVF allows (and still get good prints), but you can set fast linear speeds in the slicer, which will be used when possible, but they will be ignored and capped to lower speeds for parts of the print where the MVF would be exceeded - so you could just leave PrusaSlic3r speeds set to 0mm/s and allow it to set speeds automatically. For PETG, with the other settings above, I use an MVF of 9mm³/s (for other materials that I've used, at their respective temperatures, retractions etc. - EDGE 10mm³/s, PLA & PLA Pro/+ 11.5mm³/s, TPU 6mm³/s, Nylon230 6mm³/s). I also cap first layer speed to 50% of the speed of remaining layers. If you use cooler temperatures than I do, you probably need to reduce the MVF value.

Additionally, if you haven't done so, enabling Linear Advance and taking the time to calibrate it is useful. In the last week, I swapped out the Trigorilla control board, for which I was using Marlin 2.0.0 bugfix, and am now using a Duet 2 WiFi with RepRap V 3.0 firmware. I used the Marlin Linear Advance test tool to print calibration patterns for both Marlin and RepRap setups (RepRap calls its version "Pressure Advance"), but the resulting K values seem to be the same. I'm using a K of 0.45 for PETG, EDGE & TPU (0.25 for PLA, I haven't calibrated for Nylon230 yet).

I haven't tried this, so I have no direct experience, but if you change from the standard brass nozzle to any material with a lower thermal conductivity, like stainless steel (brass 109W/mK, SS ~8W/mK), the ability of the nozzle to melt the plastic will be reduced (slightly, because the distance from the heat block through the nozzle is short). MVF is therefore also likely to be reduced and print speeds will be slower. A copper heat block and nozzle would have the greatest heat flow (apart from silver - I haven't tried this either!)), but a volcano or super volcano would beat this hands down, with MVFs for PETG of around 24mm³/s & 100mm³/s, respectively (My son has a volcano setup on his Core XY printer and can print a Verkstan visor in PETG in 9 minutes (with a 1mm nozzle). It takes 32 minutes with my setup!

I apologise for the epistle. I hope it's some use.