The general rule of thumb is, at higher dilution such as 1+3 (as opposed to stock) the negatives will be sharper and contrast will be gentler but the grain will be coarser. If fine grain is your primary goal then you should stick with stock solution. However the differences between stock and 1+3 will be subtle. And you can also use 1+1 as your working dilution which might be a good compromise.
In one liter of Perceptol stock solution you can develop five rolls of 135-36 film or five rolls of 120 film or 25 sheets of 4 × 5" film. Use as much stock solution as you need to fill your film tank, then pour the used solution back into the one-liter stock bottle. For the next roll (or after 5 sheets), increase development time by 6 %. If you use 1+1 or 1+3 dilutions for one-shot development then you should use at least 200 ml of stock solution per roll (or 40 ml per 4 × 5" sheet)---that means at 1+3 you'll have 800 ml of working solution for each roll of film; will your film tank handle that? At 1+1 you'll have 400 ml of working solution per roll which is a convenient quantity ... and no hassle with used stock.
If you want to use stock and you have prepared more than one liter of stock solution then it's best to separate one liter of current working stock from the rest of the stock and use that for five rolls (or the equivalent number of sheets).
By the way, Ilford ID-11 and Microphen developers will yield twice as much film as Perceptol, i. e. ten rolls of 135-36 or 120 film or 50 sheets of 4 × 5" film per liter of stock solution. Using diluted one-shot working solution, 100 ml of stock solution per roll will do.
-- Olaf
