That is not correct, as can be seen from all the discussion on this forum about how to squeeze out a little more iMac performance. E.g, using 3rd party RAM with faster timing, or SSD plus an external drive vs Fusion Drive, etc.
...but we're not talking about
faster 3rd Party RAM or SSD vs. Fusion. We're talking about Apple's eye-wateringly overpriced 32 to 64GB RAM upgrade and equally expensive (but maybe less overpriced for high-speed PCIe SSD kit) 1GB SSD to 2GB SSD upgrade, which is the only way to push the iMac price up to iMac Pro levels.
There are diminishing benefits to increasing RAM but it generally helps some.
The important thing about diminishing returns is to know when to stop throwing money at them. The 64GB and 2TB upgrades on the iMac may shave a few seconds off your time, but are so expensive that they're unlikely to "pay their way" unless your workflow is
genuinely RAM or disc-limited... and in that case, I'm sorry, but a 32GB/1TB iMP will probably be RAM- or disc- limited too.
This can be seen from this study of performance benefits of various Mac RAM configurations:
http://www.macworld.com/article/203...ifications-of-additional-memory-on-a-mac.html
All that article proves is you'd be bonkers to try to Photoshop large files - or allocate 4GB of RAM to a VM - on a MacBook with
4GB and a spinning HD (of the none-too-fast variety that Apple like to fit). The latter will absolutely guarantee that things will grind to a halt as soon as you start swapping to disk - something that SSDs help with enormously, not because of their size or sustained transfer speed, but because
any SSD has order-of-magnitude faster seek times than spinning rust.
The closest test they did to your 4k editing was the Handbrake test - which was barely affected by
quadrupling the RAM. Probably means that it was limited by that slow HD. Now, I know that Handbrake can happily max out all virtual cores on an i7 so that's one thing that the iMP's 8
real cores should eat for breakfast -
if your disc storage can keep up.
Our main storage is on external Thunderbolt arrays but 2TB SSD would enable an iMac to hold a few more things there, so this would help some.
If your workflow is really being throttled by external HD storage or lack or RAM on an iMac
it will still be throttled by external storage on an iMac Pro and those extra cores will go unused. It might be that improving your external storage is the key to improving your workload...
The amazing thing is a top-spec BTO iMac 27 overlaps with the cost of an entry-level iMac Pro yet is not nearly as fast.
...as I said, be
very careful assuming that the
per-core performance of the iMP will be night-and-day better than an i7. Some of that premium will be for stability and extra PCIe lanes and the rest depends on making efficient use of the extra cores and GPU features.
We really know squat about the iMP's performance at the moment. Probably there will be some jobs where a 32G/1T iMP leaves a 64G/2T iMac in the dirt, and others where the extra RAM and/or SSD turns the tables. Until we start to see some actual tests on the iMP its anybody's guess and the
sensible comparison is to compare the same RAM/SSD configurations.