I'd be skin and bones at 170. I can stay at 200 and still be under 16% bodyfat. OTOH, maybe it will scale. Get it to a base payload of about 250 lbs, and I'd give it a try.
If you want diet that tastes like sugar, there are some options:
For the big producers:
Pepsi's Aquafina FlavorSplash waters - grape, raspberry and wild berry, use just Sucralose, (a 0 calorie substitute) last I checked. No other Pepsi products use just Sucralose to my knowledge, but rather mix it with something else such as Apartamine and/or Ace-K. Ace-K is a big issue for diet soda safety, in that it's not commonly mentioned and less seems to be known about it than other non-sugar alternatives. Sucralose occasionally tends to upset digestion, but mostly in people who are consuming quite a few cans a day, and switching over to it gradually helps - 80% or more of people who do a lot of sodas a day, do OK by gradually switching and giving the digestive system a couple of weeks to adapt. There are no Coca-Cola products with just Sucralose, as far as I can tell. Diet-Rite cola is usually made with just Splenda (sucralose), as is Diet RC cola. It doesn't hurt to check the labels on any of these, as there may be some canned or bottled in other countries than the US that isn't exactly to the US formula.
Honest Fizz is a bit pricy, running about 1.20$ US a can. It's sweetened with a mixture of Stevia Leaf Extract and Erythritol. Erythritol is a complex alchohol and means one can has about 5 grams of carbs. (that's not a lot, but it's a few calories - about 30-40). Just like Sucralose, some people get increased gas or even cramping from Erythritol, some don't, at least if they aren't drinking eight cans a day. Just because one of these substances causes discomfort in some users doesn't mean the other one will affect the same people.
For pure Stevia sweetener, you could try Zevia, which now has 15 flavors, including Mountain Zevia, Doctor Zevia, and Caffine Free Cola.
I don't get paid to plug any of these. I don't own stock in them and nobody with them has asked me to say anything about them.