Omni ...
Reading this thread it seems that you've been given numerous suggestions and techniques that will give you the result you want. In short, if you've got the taste down to where you like it, the rest is really up to you to experiment with time and yemperature. It's really that simple. No one can give you the answer since everyone's stove, fryer, thermometer may be somewhat different. Here's what I'd do: get your oil up to 350-degrees, put in a certain amount of fries, say 6-oz, fry for ten minutes. Now look at the results, taste the results, feel the results. Adjust time, temperature, and amount of fries until you get the results that YOU like.
I work in photigraphy. When using film, we'd have to calibrate the exposure index. If we wanted perfect results, rather than "close enough" we'd start at a certain EI, make several exposures that were greater and lesser around that point, and check the results. Then, when we've found the best exposure, we'd then calibrate development time, developing more or less to get that to be precise. Then, once we had the proper exposure and development time for a given emulsion, we were set - unless we used a different camera or light meter, as each could produce different results. NO two were exactly alike.
Now, say I found the perfect combination, and gave those results to a buddy who lived across the country. S/he could use my results as a starting point, but if greater precision was needed, s/he'd still have to run his or her own tests. The cameras would be different, the way the development chemicals were mixed might be different, as might the quality of the water (harder/softer), his or her timer may not be exactly as mine.
Now, go out, get some fries, and experiment until you get the results you want. Oh, and by the way - your idea of soft may not be the same as someone else's idea of soft. So even if someone gave you exact times, temperatures, precise amounts of fries and oil, they may still not get results that satisfy you. You may still prefer your fries to be more or less crisp.
In another thread I asked about baking a frittata. I got several suggestions and ideas, and one or two recipes. The rest is up to me. Tonight I made a frittata following a recipe that I was given. The results didn't satisfy me. But it was a starting point. Now it's up to me to experiment a little with times, temperatures, and amount of ingredients to get exactly what I want, using my equipment, my ingredients, and the amount of ingredients that I have on hand. It will take a while to perfect the recipe for my situation and tastes. I may have to make the dish a few more times in order to get predictable, repeatable results.
Shel