I wasn't going to comment, but being almost at the end of changing everything you're doing right now, and for the same reason (to get setup before I go back to using the IT), I should pass along what I've learned. I'm also a lefty, and started with the same specs as you on most of my equipment, except I had 1/8 left lateral. I'm down now to 4-3/8 and 4-1/4, and have gone from a max reverse of 1/4 to zero forward now and zero lateral. The ball feels MUCH better in my hand, but I'm throwing it lousy. I've also developed a really bad callous and split skin on the inside of my thumb. I actually printed this PDF tonight and it pointed straight to 1/8 rt lateral (remember, I've been 1/8 left with no problems, and now zero with a callous). 2 minutes ago, I picked up the can again and now it's pointing straight to zero... Sigh. It's not the same in repeated testing, and it's still not where I was when I know I had no split skin for years...
There are a few things to pass along....
1. The can is a guide, not confirmed, and don't be surprised if you change lateral and get a callous, like I have. In that respect, I've progressed backwards, no doubt about it.
2. In my case, I've dropped 1/4 on span, and it's too much.
3. Here's the strangest one... I started with 61/64 thumb. Now I'm using 15/16 and it's too large. I don't know what others will say, but I'm convinced that I was bending the thumb, therefore needing more room in the thumb hole. As I fix span and pitch, at least for me, I have to change thumb size.
Bottom line, I've screwed around too much, but I learned a lot, and now need to drill a few more slugs to test final changes, because I'm a bit worse off than when I started. I can't believe how much more comfortable the ball feels though, and I'm confident I'll be happy with the results in the end. Be ready for some frustration and learn when to stop screwing around with it.... That's what I failed to do.