I am using an iMac, and it becomes slow when running Dorico with BBCSO pro template.
Which iMac? How much RAM? Does it have a mechanical hard drive? Large audio samples use a lot of RAM and CPU (and need to load from disk).
You definitely want a 4-core CPU (or more). Some of the older 21.5" iMacs had only 2 cores. 16Gb is probably a minimum. Surprisingly, Apple continued to put spinning mechanical drives inside many iMacs until very recently. These are very slow and cause ‘bottlenecks’, while everything waits for the drive.
Using an external SSD via Thunderbolt, or even USB, should be much faster.
I would also add, if getting a new Mac get one with the M1 chip. Even with the RAM limitation (which I argue is quickly becoming irrelevant) the M1 is the way to go.
Frankly I would answer the question in a different way and focus initially on getting the BBC Pro performance up to scratch. This library is pretty demanding on the system if you’re using anything like all the microphone positions and are using a full orchestra. It is very likely if you reduce the mics to a minimum and run the library in Vienna Ensemble Pro in decoupled mode so Dorico can effectively run independently from the library that your system will be able to cope better. How well obviously depends, as @benwiggy says, on exactly what you have at the moment.
I ran Dorico + BBCSO pro on a top drawer 2013 Mac Pro with gobs of RAM. It was an unsatisfying experience. Note entry was slow enough to make it not worth it. Moving it to VEP improved things a bit, but it was still slow enough to get on my nerves. Finally switched over to a top drawer PC and BBCSO is as nimble as as NotePerformer or HALion. So basically, get as much as you can, and even then I’m not sure it’ll be satisfactory.
Apple specs, and then under clocks and under builds their systems relative to the parts used, basically they target general consumers and favor power saving over performance. The parts chosen are much below what you’d get elsewhere. The latest Mac Pro doesn’t count for anything, it’s a trophy piece for the company.
So hard to say … I’d expect though that you’d want one of the recent top end iMacs, as that’s the best you can get in an Apple, but ultimately you’d better served with a high end PC for less money, if you can break away from Apple. But who knows, maybe a recent iMac would be OK.
FWIW if you do go PC and need performance, AMD Threadripper owns the performance CPU, and NVIDIA owns the GPU.
This is my setup:
Model Name: iMac
Model Identifier: iMac18,3
Processor Name: Quad-Core Intel Core i5
Processor Speed: 3.4 GHz
Number of Processors: 1
Total Number of Cores: 4
L2 Cache (per Core): 256 KB
L3 Cache: 6 MB
Memory: 52 GB
Well, it’s certainly not a shortage of RAM! You don’t say what your storage is, but if it’s a Fusion drive, then that means a mechanical drive is in there somewhere.
Otherwise, the hardware should be fast enough, so there may be some other issue. How slow, exactly? And when is it slow - just in loading the samples, or at other times. Are you using Condensing?
I have a 2018 Mini, and BBC SO (Discovery) runs fine.