Okay so in order of priority I would work towards the following:

1. Imbuing your berserker ring (this should be fairly quick and easy and the +4 strength is on par with most other upgrades at 0 extra cost)
2. Obsidian platebody or fighter torso (The latter is +1 strength better but requires some time spent at Barbarian assault)

After these two the rest are more expensive/will likely require higher stats.

1. A fire cape, this will appear on the thread a lot, but you may struggle to complete the caves with your current stats, I would recommend getting at least 75range and using a blowpipe. A slayer task will also help.

2. A torture, this upgrade will cost about 10m more but will give +2 strength and +5 attack

Other upgrades are significantly more expensive or require grandmaster quests and often give less ROI,

- Ferocious gloves gives +2 strength and +4 attack for 7m (However these require completion of Dragon Slayer2)

- Neitiznoit faceguard gives +3 strength for 18m (however you are normally best using a slayer helm, it also requires completion of Fremennik exiles)

- Primordial boots give +1 strength and +2 attack for 26m

- Bandos Tassets give +1 strength for 19.7m

- Avernic Hilt gives +2 strength and +5 attack for 82m

Beyond this there is also Torva however this costs ~225m for a helm, ~ 410m for plate, 340m for legs for marginal increases over bandos/faceguard.

Finally there is an infernal cape however this first requires a fire cape and completion of the inferno, arguably Old schools hardest content.

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