Well pro'lly you have a low evader level, so be prepared to pay very much in armor decay. On ghost whith such a low dps gun i estimate 50% defensive costs.
My advice is save the peds and skill up on something smaller ( e.g. Exas )
Use the SIB gun you have maxed. For now stay with the Opalo. When you have maxed the m2a go for it, slap an A102 to it and go for mobs like Caudatergus,Cornudacauda, Bery, Faucervix and such.
Even small Argo is worth to mention.
When you are close to maxing p4a with Your pistoleer level you have a weapon which gives you a good bandwidth of huntable mobs. Longu,Atrax, Drones, Argonaut ..... ( many more out there which can be killed with it )
When you have a good Evader Pro Standing you can Hunt Troxes in Hunter + 5a Plates and have a fair percentage defensive decay.
I think sufficient dps for Atrox is at very least ( better in team ) Amped P5a ( due to the high Agression and Triple dmg Type = high decay when slow killing ) better more dps.
I would not go for ghost. Imho too expensive in terms of decay for low skilled players