I’m a little overly curious so I hope you don’t mind if I ask a few question? Like, was this a home made project or a purchased hull project. Your alterations to the water line suggest additional weight; do you know your displacement/length ratio? This calculation, I’m sure you know, will help define your practical hull speed. Is the steel rolled and welded, 6mils perhaps? The additional weight would obviously have lowered your “M” point, have you calculated your righting arm. Just curios.
Purchased hull project, straight-forward welded construction with a single chine. In principle many major items necessary present, in practice years of poor prior maintenance, some theft, and further (major) life complications made it into an even bigger project that it was originally. Total refit inside appropriate, and as it turns out renewal of all interior systems (incomplete but in progress). Picked up welding (through trial and error and asking questions of people who know how) to add a bulk head, repair the hull (cut out some sections and put in good plate), create steel (ultimately to be watertight) doors, etc. - I'm sure you know how it goes if you take on a boat without much ample funding, you learn how to do things yourself or you fail - there isn't a middle road.
Displacement/length ratio right now should be around 290, I anticipate a value at least 350 when finished, 390 at the theoretical upper end (depending what it takes to set things up where I feel they're right, and on the limits set by the waterline which is about as far as I'd care to cut freeboard ie I want some!).
I did calculate the righting moment as the vessel originally sat one night in the water (literally lifted a ton and a half of water up by hand) to tip it over slightly - arrived at righting force of nearly 8000 ft-lbs or 10850Nm at 5 degrees of list. Have not been able yet to find another boat owner who has any idea what their initial righting moment is for comparison and need to repeat the exercise (hopefully with a pump next time) now that I changed so much.
The new waterline is my best guess as to what I need worst case, arrived at by estimating my anticipated additional displacement for the approximate cross-sectional area and allowing for the addition of ballast (the vessel has almost none, which cannot be right) as well as all the new steel, batteries (almost a half ton in batteries alone), etc.
I cannot pretend to any nautical knowledge any more than any other sort of knowledge, but all things being equal within a few weeks I'll have stared evolution in the face to see if I'm fit enough to survive (I have to relocate internationally before completing). Then I might put a bit more about the project in another topic on the forum (the one to do with building things).
Unfortunately (and with a nod to the original point of this topic), I might have no option but to run on the engine for at least several days - the current weather forecast is way beyond what I'd dare tackle with sails given inexperience and standing rigging in serious need of renewal (the materials I have, the time I do not).