What is your staff currently using? The processors have come really far in the last years with Apple chips, so anything will be a huge upgrade.
If you already have good monitors, then I would get M4 Mac Minis as they will be powerful enough for 99.9% of what we do in screen printing, especially if you are still mostly vector graphics. If you have someone who handles sim process separations you could get them Mac Studio or Mac Pro but they are overkill for what our industry does in my opinion.
If you want your staff to be mobile, then a Macbook Pro or Macbook Air with recent chips are all powerful. I personally work on a Macbook Air M2 with 16gb ram and it's powerful enough for like 99.9% of things and that .01% I can live with just moving slower on those graphics.
If you don't have monitors already, then I personally like the iMacs as they are a good value and a good screen. May not be super color accurate but again I think for my guess on your client base it may not be that important.
I'm cheap, and Mac's lifespan is much longer than a PC espeically with the new chips. I feel no need to upgrade my 2022 Macbook Air M2 even when using new features in Photoshop that may go a little faster. For what we do (copy / paste onto a mockup / assign spot colors for separations) I don't think it's necessary to have the most powerful computer / processor.
I think at the time I went with the lower spec processor and more RAM like Admiral said, but again I'm cheap and at the time Macbook Pro was behind on updates so I got the Air as faster processor and cheaper. Can look here -
https://buyersguide.macrumors.com/#mac as they have notes about releases and when you should or should not buy.
I think in most instances you may be better to run a RIP on a PC that runs on the network on a dedicated PC for that, as I think RIPs will have more support for PC than Mac and if the RIP is the thing forcing the upgrade it could make sense to change that over now instead of updating 6 macs. It's not a big purchase but Apple does have a business division that you can get some discounts off retail from that you may want to look into.
Post what computers they are currnetly using, if you don't know how just hit the apple icon in the top left and the first menu is "About this mac" and it will tell you the year, computer, processor, ram, operating system.
Adobe's trying to move a lot of the AI and new gimmick features to cloud processing anyhow, so long term having a faster processor may not even matter as much in a couple years. But for most of the illustrator, spot color mockups, separations, the lowest power mac mini will be fine for 95% of stuff.
Don't think you need to break the bank.