well i was thinking about hl8 not hl6 ^^ you will see the dmg difference is really big and well for the ambu more dmg you deals better is the retun ( ambu got a big hp regen )
And sry for your bad return atm
i think your uber (1k+ ) will come at run 30-40
gl
H400 is quite eco, 2,905 DMG/PEC with A103. HL6 only 2,868 and HL 8 only 2,798.
Up to Mature the Ambus are managable without probs with an H400/ P5.
Would advice getting an A104, P5 would make 2,919 DMG/PEC, HL6 2,878 and HL8 2,802 with that .
Return is a bit based on damage done, but this does not mean that a fast kill gives better loot. You can do more damage when the mob regens a bit, but overall the average is not changed by that.
Tricky part is to not have to spent too much on markup for the guns and not too much on decay for armour and FAP.
In my opinion it is better to get more skills out of a gun and get the gun as cheap as possible. For defense skills you need to get hit, with a fast kill you would get less skills and in the long run pay more decay (because the defense skills would go slower).
Slow gun gives more defense skill, but costs more in repairs, still lower repairs costs faster in the future.
...a lot to consider
But A104 is surely a good investment