I've unlocked maximum prestiges on all productions 50 days ago - I have now gathered the data from this period to break down the profitibility of maxed productions.

The Investments
Let's start with the total cost of unlocking all production prestiges, taken from Shippuden06's guide assuming the minimum/efficient number of productions unlocked per prestiged level.

I've also included the cost of getting the rep required (15m) from nothing but hits bought from rep farmers at maximum efficiency, which is currently 1,440 rep hit at £1,500,000 per hit. In reality people will make rep from other sources such as job and missions, and extra rep during church events, making this the theoretical maximum only.

	Total Invested
Weed Field	£5,334,546,000
Cocaine Factory	£1,677,760,000
Alcohol Still	£1,997,225,000
Doctors Office	£60,450,000
Street Production	N/A
15m Rep	£15,625,000,000
Total (with rep)	£24,694,981,000

The total number of hits necessary is around 10,400, which is around half a year of energy. In practice, church events and standard jobs can increase rep gains significantly - I've increased from 10m to 15m rep in exactly 50 days as an example.

Daily Profits
Here's the breakdown of daily input, output and total profit using current market prices:

Production	Cash per day	Items per day	Unit Value	Total Daily Output Value	Daily Inputs	Unit Value	Total Daily Input Value	Net Profit
Weed Field	£3,768,156	224.26	£140,000	£35,164,556	108	£150,000	£16,200,000	£18,964,556
Cocaine Factory	£5,274,007	25.84	£1,200,000	£36,282,007	66	£200,000	£13,200,000	£23,082,007
Alcohol Still (Cash)	£1,824,229			£1,824,229	28	£350,000	£9,800,000	£110,164,229
↳ Corana Beer		2.8	£200,000	£560,000
↳ Blancoda Tequila		6.66	£1,000,000	£6,660,000
↳ Repose Tequila		6.4	£3,000,000	£19,200,000
↳ Anejo Tequila		5.74	£6,000,000	£34,440,000
↳ Raicilla		4.04	£14,000,000	£56,560,000
↳ Mexcal Beer		1.44	£500,000	£720,000
Doctors Office (Cash)	£75,847			£75,847
↳ Bandage		9.58	£90,000	£862,200				£6,155,047
↳ Small Medical Kit		8.46	£150,000	£1,269,000
↳ Basic Trauma Kit		5.26	£200,000	£1,052,000
↳ Large Medical Kit		6.56	£150,000	£984,000
↳ Large Trauma Kit		4.78	£400,000	£1,912,000
Street Production	£10,168,246			£10,168,246				£10,168,246
GRAND TOTAL	£21,110,484			£207,734,085			£39,200,000	£168,534,085

In short, max prestige productions make about 170m in real profits per day or around 205m if input materials are obtained from jobs.

100% (untainted) cocaine and 100% tainted cannabis were chosen as production options as the most profitable options during this period. For max prestige weed field productions to be profitable, as a rough rule of thumb, bags of fertilizers need to cost less than the double of the higher priced options between tainted or untainted weed.

ROI
Now we can compare the yearly return on investment of each production type as well as the overall 15m strategy:

	Total Invested	Yearly ROI
Weed Field	£5,334,546,000	129.8%
Cocaine Factory	£1,677,760,000	502.2%
Alcohol Still	£1,997,225,000	2013.3%
Doctors Office	£60,450,000	3716.4%
Street Production	N/A	N/A
15m Rep	£15,625,000,000	10,400 hits; about 6 months
Total (with rep)	£24,694,981,000	249%

The data confirms the folk wisdom in our community that Alcohol Stills are very profitable, with Doctors Offices having an even better ROI (but with low investment and low returns).

What might come as a surprise to many is that even the worst investments, Weed Fields, still produce a very high rate of return compared to other late-game options with current market prices. The 5.3b investment (assuming the rep is there) breaks even in about 8 months.

Should one only make rep from bought hits, the total investment of 24.6b would still break even in about 5 months. In practice, a lot of the cost can be avoided by trading rather than only buying hits once one has a good enough level - but this requires leveling up. Being able to do legendary daily, weekly and monthly attack missions can also reduce costs, as well joining a cartel that has a rep-based payment scheme.

The rep can also be obtained for free from normal gameplay over the course of multiple years, however these will be years of losing out on at least some part of the 61.5b year return that could be obtained from total commitment.