Regardless of what you have done, the only person constraining you to that method, is you. I've taken a different direction, been reading up as much as I can and gathering components but I haven't actually hand loaded a cartrige yet this year, my prior hand loading experience was in 1983-1984 with a Lee Loader kit and a factory new S&W Model 13. It's part of my basic nature confirmed with Birkmann assessment when I was sent to executive charm school in 2004. Thee were others whose basic nature are to charge head first and maybe look back once an unexpected obstacle or development occurs. Neither is right, nor wrong. I had a NRA Metallic Cartridge Reloading class scheduled end August that got bumped to end October. I want to find out what I still don't know in a structured setting before I actually start hand loading again. I had a self-inflicted close call in 1984 that fortunately occurred while plinking with a more experienced coworker, which could have gone very, very badly if I'd been plinking alone that day.
There are extemists, the foolhardy that charge ahead no matter what, and those who turn study into the cliche'd "paralysis by analysis" never taking action. Neither one of us fits those extreme mold in our approaches. There's room for information exchange and broadening in both directions.
I have a copy of the Hodgdon 2020 Annual Manual, it has load data for 158 grain lead semiwadcutter bullets in 357 Magnum, but not using Alliant Unique powder. Lee's manual more or less collates published data from other sources into one spot at one snapshot in time. My copy has data for 158 grain copper plated in 357 Magnum, but only for Ramshot Zip and Solo 1000 powders.
One thing I've found is the more reading I've done, the more valuable I've found having multiple references to compare and contrast has become - for me. You might try it and find what you need to move forward in one particular area after looking at maybe two additional references. Some sources have more explanation about why's than others, some I've had to ferret out nuggets here and there for me from all the chest beating about how superior that brand's products are than all competitors - past, present, and undoubtedly the future.
You took the step to openly ask questions. I did my best to help with what I see and have come across, despite not having hand loaded a cartridge in over 35 years. You took it in a constructive way - not everyone would, not everyone would have even posted a question. You haven't blown yourself or any firearm yet, and based on that, you're still available to ask questions. No harm no foul on results, but thee are alternative methodologies available.
Some folks don't use published load data very much preferring to use software like Quickload for their objectives. I don't plan to purchase Quickload any time soon for myself until I've been handloading from published data that's often available at low o no financial cost. I've seen some folks make a Quickload run for someone who doesn't have Quickload for a combination of components not found in published data and may not exist in published data - like the combination you've been using. Just another avenue. There's subscriptions to websites like LoadData.com some folks use. Those can give some sort of "sanity check" but have their limitations and assumptions as well.
If those velocities haven't been excessively leading your barrel using plated bullets, you're not being constrained by the reason Speer publishes as their upper velocity limit - different set of conditions. What upper elocity limit does Berry’s Bullets recommend for he ones you're using, and how are you measuring or estimating the muzzle velocity of your loads? The difference in hardness (malleability) of a copper or gilding metal jacket vs copper plated lead vs plain unjacketed lead and frictional effects during travel from cartridge mouth to muzzle aren't the same.
There are some real considerations in some instances for jacketed vs non-jacketed projectiles. If you read more of the text you'll see warnings about some jacketed bullets at certain velocities an leave the jacket in the barrel but the lead core continues on - so probably punches a hole in the target leaving the shooter no reason to suspect firing the next round will result in a high speed collision inside the barrel. There's also conditioons where there's so much ot as it cuts a non-jacketed bullet around its perimeter on their way along and out the barrel in some cases. I'll say up front though I've really only skimmed most of the information for consideration on non-jacketed bullets because I personally don't plan on using any for the near future anyway. But I've become aware there can be unexpected results due to differences in bullet construction - jacketed vs non-jacketed, specialty Trophy Bonded Bear Claw & Sledgehammer Solid bullets vs their direct competitors (also monometal bullets vs lead jacketed bullets) all sorts of things I'd still be pretty much unaware of if I'd just continued purchasing factory loaded ammunition.
If you're ever in the Alamo City area let me know, and we can compare notes on where we're at and what we've done and what we think is next and spend some range time together. Even before COVID-19 my travel has been considerably reduced.
And TMJ's (among other Speer offerings) are not actually jacketed, (in the traditional sense),,, but instead, thick plated. 
