Id come at this from the other angle. I think everyone thinks about what chips they want but honestly Id be thinking how much XP per hour do i want to earn. I havent looked at the chip values in game obviously but id be thinking add up the APU total of the armour i want to wear (lets say its +25 apu for round figures) and then id look at how many brain slots do i want to use up to gain that armour vs how many could i change for X no of chips (old APU 2 and 3 chip could give me more APU for example). Then I would look at the % damage on my best value skill. All of this is number crunching (some people love this obviously and it is one NC's finest points) but i would honestly go the other way and spec for my target in all fairness.

Id stary asking myself the following: Where do you want to go levelling? what do you want to achieve? fastest way to cap? easiest time of it? less downtime (death)?

Con setup on APU is probably really one of the easiest things to manage, you dont have many points so its not like you can make massive screw ups. if you balance your con set up based on what you want to achieve above (ie what mob do you want to farm or what dungeon you want to go in) then you can always lom later as you will have plenty of XP over the cap.

If youre levelling in a dungeon i think chaos caves is still ok, not sure about swamp caves. But basically its poison resistance (or it used to be). If you want the firemobbing (with some "long range" spells) then obviously pack on the fire resist. If regants corridor is still ok then I think (last i played) movement and staying ahead of the shambling blokes is probably better, so more transport and more psi boosters are probably the way forward.

Some of my information may be out of date by now obviously but I think the methodology is probably solid. I would ask around in game and find out what the people say and plan according to that specific type. If it doesnt work, adapt your strategy and go elsewhere. I understand now that armour plays a huge role in resists (not sure if this is PVE or PVP) so that makes it even easier, just swap out your armour for a different set and crack on. I know the map hasnt changed much in the last 10 years so those things arent likely to be an issue. Decayed horrors will still sit at Gabanium mine hopefully etc.

For me the emphasis on APU levelling was always about the largest group of mobs in the smallest space possible - circle strafing regants boss room being the epitome, or barreling launcher cyclops woc mobs in the tunnels. However if these places are no longer viable for the solo runner then gearing towards a specific dungeon (El Farid, Chaos cave) might be the better option.