So small for me is somewhere between Z/Ninja400 and SV650?
What about a Street Triple 675? That's 106 hp. 416 lbs.
Is there a weight/hp sweet spot to shoot for?
It really depends on your goals.
If you want to really learn how to maintain corner speed, brake later and get on the gas earlier. I'd say you want something with a max of around 75 HP. I wouldn't worry about bike weight as a smaller bike will weigh less but my guess is that it will be sub 400 pounds and closer to 300.
Bottom line, you are looking for a bike that you can learn to ride to the limit.
One note though...plan to upgrade suspension on it when you get it. You are a big guy. You won't have confidence on a bike sprung and valved for someone half your size.
I'd really suggest buying used. This isn't a bike you'll keep for years. It's a bike to learn on, and then replace.
I saw a pair of SV650s on FB marketplace for 3K. Both had aftermarket suspension. Something like that gets you in cheap, allows you to learn and then you essentially sell for what you paid for it afterwards.
I realize you tend to buy new so you don't have to worry about repairs and such. You can do that too...it's just going to be expensive to buy a bike that you won't really keep that long and then spend 2K upgrading suspension and adding track options like rear sets and clip ons.
You may be different, but for me, when spending money for new, I'd tend to look for a bike I like and might want to keep rather than a utility based learning tool. Having a bike I really like that is new and shiny is a bit counter productive to the goal of having a bike I am willing to push and risk a bit more.
It's a bad example because it is not in the smaller bike category we are talking about, but I've never taken my Super Duke to the track. I'd really like to ride it hard on the track but I know I'd ride it conservatively and would likely be way faster on my track bike that I'm not really worried about. I'm certain I wouldn't progress very fast on the SD as I would ride it quite conservatively to ensure I brought it home without incident.