Hello!
I was testing different setups with upgraded ranged RK weapons-XXX on my lvl 200 froob soldier. The only weapon line I've found useful was 1-handed ranged energy due to low requirements for capping burst (900) and fling shot (900). I was able to equip ql 287 El Diablo C05 and got some decent dmg output (ask Murmandramas ingame if interested). Well, variety of upgrader RE weapons is poor - only 3 different 1-handed guns plus 3 different 2-handed guns which are worse than each 1-handed RE. I don't really get the logic why 2-handed upgraded RE weapons require so much more burst (1525) and fling shot (1700) for the cap - it's unfroobable and noone with at least SL expansion will deal with upgraded RK weapons.
Pistols: there are lots of upgraded RK pistols-XXX, but due to only one special available (fling shot - cap at 900) they are useful only for lvling at low lvls. For the endgame this is not an option.
Assault rifles: they've got 2 specials: burst (1675) and full auto (2630) both impossible to cap plus weapon speed itself 1.8/1.8 is terrible for assault rifle. Plus full auto shiny cluster and assault shiny cluster ocupy the same spot in implant. I've even tried Subturbine C0C on my paid lvl 203 soldier and was wery disappointed.
SMGs: like pistols upgraded SMGs got only one special (burst) whichs is much hadred to cap than with Blackbirds and noone except fixers and soldiers will chose SMG as primary weapon. Like RE 1-handed SMGs have low burst requirements (1000) for cap than 2-handed (1375). And it gets more complicated because Shiny SMG cluster and Shiny Burst cluster ocupy the same spot in the implant.
Rifles: well, upgraded riflis got nice regular dmg plus some of them have stunproc (very low trigger chance) but requirements to cap aimed shot are impossible (2267).
Bows: Upgraded bows got lower aimed shot cap requirements than rifles (2007) but nobody uses bow as the main weapon on RK due to lack of bow buffing nanos and gears. Plus upgraded bows are useles for hot-swap in pvp due to high requirements.
Shotguns/grenades: these 2 types of upgraded RK weapons are quite similar and useles. Both have only 1 imposible to cap special - flingshot (1700 for shotguns and 2820 for grenades). RK traders do not have perks which forces them to use shotguns (ma-trader got much better dmg output for example)
In total upgraded RE ODs all other upgraded weapon types because of fast specials.
My suggestion is to merge upgrade types between weapons: for example availability of SMGs/Pistols/REs-C05 (burst + fling shot) or Pistols-C02 (aimed shot), SMGs-C0C, Shotguns-C04 (burst). Also special attacks cap requirements should be lowered to RK reality.
Weapon choice for making them upgradable is quite weired in my opinion because in general most of them are pretty much the same except the looks (for example a bunch of C01 pistols with proj dmg type). On the other hand there are lots of other awesome/unusual weapons which deserv to be xxx-upgradable like IMI-Tellus TT (and all other weps crafted from Sealed Weapon Receptacles), Inner Circle Strategic Flamer, Pain/Reign of Patricia, Nophex Plasma Destroyer, Prelude to Chaos and other RK weapons wich are hard to get. Hardly obtainable RK weapons with some XXX-upgraiding could be a good endgame weapons for TL6 with ~1350-1400 weapon skill requirements, QL special and Nodrop flag.