Help working out the optimal strategy for a game please :)

I've been playing a game called Game of Thrones Ascent on Facebook. Recently they released a new Tales challenge mode. Players who rank in the top 2500 get a free 25 gold premium currency which is usually very difficult to acquire (3 gold per week for logging in each day) and these events occur monthly and last for 5 days

In these events the player gradually accumulates vigor every 5 minutes up to a cap of 60. 20 vigor is required to make an attempt at the challenge. There are 3 difficulty settings and completing all 5 stages of one unlocks the next difficulty. These are normal, hard and epic. Victory rewards renown and other rewards and the player with the most renown after 5 days wins. Players are ranked according to renown. it seems I will need about 18000 renown to rank in the top 2500 but this number seems to be dropping as the only players to get anywhere near the top are the ones who pay real money for more attempts, but as I say I only need to rank top 2500 without spending money for the 25 gold reward

Normal gives the least renown, hard gives about 5 times as much as normal, and epic gives 50% more than hard. Each challenge attempt is split into 3 stages. The player has a team of 5 "sworn swords" and are presented with a problem to pass and told to pick 2 sword swords to face the challenge. This happens 3 times per stage. The details about how these challenges happen aren't all that important as I am already following the optimal strategy for that. The only point here is that each time a sworn sword is used it accumulates fatigue and at 3 fatigue it cannot be used, but each time it isn't used it drops 1 fatigue. Sometimes a failed roll accumulates multiple fatigue. This is only a problem when the game keeps throwing the same challenge requiring the use of the same sworn swords until they are exhausted and the challenge cannot be defeated as it keeps popping up. There are 2 challenges so if a challenge pops up 9 times it's like flipping a coin 9 times and getting tails 9 times. This doesnt happen very often

Now, my probability of success is pretty stable mostly. On normal it's 94-97% per stage, on hard it's 74-78% per stage and on epic it's 60-65% per stage. If I fail 2 challenges in a stage I immediately fail the challenge and the vigor I invested was wasted. At the end of every stage I have the option to back out and take what I have accumulated, or risk it to continue to the next stage. Now I have only been playing hard since not only does playing epic mean a harsh hit to success chance but I have to clear 5 stages of hard to unlock it.

The first event I settled on doing hard mode stage 2. I was failing about 20% of the time and accumulated about 400 renown per try (not counting fails). Last time I was aiming for hard mode stage 3 and I did slightly better but I noticed my lucky streaks were getting worse. This time I am aiming for hard mode stage 4 because that gives about twice as many "keepsake" items (items used to produce rare equipment) than stage 3 and because I didn't believe I could hit rank 2500 (I got 3300 last time). However within a few days I had just passed rank 2500. However my renown isn't all that high and it seems likely I got to this rank because less people are competing. I got quite a few stage 4 successes and then I hit a bad luck streak where I kept getting bad rolls, so I decided to record my rolls

The way this works is that after I put up my two sworn swords then it gives me a % chance of success. I click accept and the game "rolls". If the roll is higher than my success chance then I fail that round. If I fail 2 rounds in a single stage I lose the challenge. I started off recording just what stage I won or lost on. Then I started recording the bad rolls and notable events like exhaustion due to facing multiple intrigue or trade challenges in a row. Here are the results since mid day before yesterday:

lose stage 1
lose stage 3
lose stage 1
win stage 4
lose stage 1
lose stage 2
lost stage 1
stage 3 roll 92 stage 4 win
stage 4 roll 86 roll 85 lost
stage 1 roll 91 stage 2 roll 82 win
stage 4 win, passed every roll except one because trade exhausted
stage 4 roll ? stage 4 win
stage 1 roll ? stage 2 roll 85 stage 2 roll 78 stage 2 fail
stage 2 roll 100 stage 4 win
stage 4 win
stage 1 roll 82 stage 4 win
stage 1 roll 85 roll 99 fail
stage 1 83 79 fail
stage 2 96 98 fail
stage 3 71 (exhaustion) 82 fail (6 trade in a row)
stage 1 78 99 fail
stage 1 97 stage 2 82 stage 3 89 stage 4 69 (9 intrigue rolls, 3 fails) stage 4 win
stage 1 94 stage 2 ? stage 3 ? stage 3 win
stage 2 ? stage 3 79 (9 intrigue in a row) 86 fail
stage 1 96 78 fail
stage 1 95 87 fail


wins 9
partial win 1
losses 16

So it seems I continued my unlucky streak, then it got more stable, then I entered a winning steak, and then plummeted into a terrible losing streak. Most of the fails were in stage 1 or 2 so I don't think stopping at the end of stage 2 or 3 would have helped, maybe meant less renown as I folded early on stages I could have gone higher on.

Anyway my question is this: What stage is optimal for me to fold at?

At stage 1 I have about a 78-80% success rate per round (so 3 times per stage) and it gradually deteriorates to about 68-70% success rate per round at stage 4 depending on how many rounds I failed up to that point. 20 vigor is consumed per attempt, I only receive my rewards if I pass stage 5 or retreat, so stage 1 gives 150-225 renown, stage 2 gives 300-450 renown, stage 3 gives 450-675 renown, stage 4 gives 600-900 renown and stage 5 gives 750-1125 renown but failing any stage will end the challenge with 0 renown. Also 7 keepsake items are given at stage 3, 14 at stage 4 and 21 at stage 5 though getting to rank 2500 or better is my priority

Something like "Stop at Round 3 as that will give the most renown over a long period of time"