How to clean up my iMac...

I would only transfer any data; photos, music, videos and documents you want to keep. Most likely any apps might be out-of-date or incompatible. I would only do fresh installs of apps I knew were compatible. Of course avoid anti-virus, cleaning, maintenance programs, etc.

My guess would be that the really important matters would have been settled or still running. So perhaps simply on an age basis. I can see your problem though; there have been times I have had to think hard.

If you have doubt you could always buy a 1Tb (or more) external HD and just file it away (in case!!!)

The reason I am asking about the specs of your new iMac before you start this rather lengthy process is if you purchased a 21 inch screen iMac with ONLY the standard hard drive.

That hard drive is a slow 5400 laptop grade hard drive that will be THE bottleneck of your entire iMac as these drives and the fusion drives for these 21 inch screen models (a low storage capacity SSD coupled to a slow 5400 RPM spinning hard drive) will be 33% slower to read and write data to (compared to a standard desktop grade 7200 RPM spinning hard drive).

If you purchased a 21 inch screen model with a full internal SSD, then you'll be fine.

If you purchased a 27 inch screen iMac, you will be fine.

i would not consider an abysmally slow 5400 rpm drive - it does everything (read/write) 33% slower than the standard 7200 rpm drive in 27" iMacs. If you don't want to or can't spend the money on an all SSD, then at least go for the 7200 rpm. I just checked the specs of the currently available 21" and a 7200 rpm is not offered, so it'd be either a 27" or an all SSD (fusion drives are difficult to control and still have the slow drive).

Anyone can see it - these are open forums (not email) where any post is visible to anyone. You can only reply though if you are logged/signed in.

7200 rpm will do nicely although the SSD I put into my MBP is really fast!

As for weeding out: if you use Setup Assistant during the install/setup of the new Mac, it will only port over your user files and any third party apps installed by you. I have to admit though, I do not know how much other stuff would be included. If you want to be that selective, going through it manually will most likely be the only sure option.

All 27 inch screen iMacs, even the brand new 2017 models have 7200 RPM drives and user installable RAM.

In the 21 inch screen models, the fusion drive is a 5400 RPM hard drive tied to small storage size SSD.

In the 27 inch screen models the Fusion Drives are SSDs tied to the 27 inch screen models 7200 RPM hard drives.

It's always been this way in the 27 inch screen model iMacs.

So , you opted for a larger screen iMac still tied to a rotational drive instead of a 21 inch screen model with a fast, nearly instantaneous 256 GBs, 512 GBs, OR 1TB SSD?

Interesting.

I can see it - I would not ever recommend a fusion drive - the very small SSD does afford fast booting and opening of apps. But - and it is a big but: the hard drive is still where all the read/write activity takes place (in other words everything you do) and a fusion drive is an absolute pain if you want to partion, re-partition, need to wipe the drive, etc, etc. It took me 2 entire days to get the iMac back to factory condition when it was determined to be DOA (for other reasons) and I needed to return it. That was my only time trying to deal with a fusion drive and I won't do it again.

MichelPM already answered your question - 21" = 5400 rpm drives and 27" = 7200 rpm (unless you opt for an SSD).

I looked at your link, as well.

Forget the Fusion drive and get an iMac with a decent capacity full SSD.

The SSD portion of the Fusion drive in the 21 inch screen models is a paltry 24 GBs SSD!

The 1 and 2 TB full SSDs maybe too expensive an add-on option, but you maybe could get either the cheaper 256 or 512 GBs internal full SSD and supplement your iMac storage with cheaper external USB 3.0, 7200 RPM hard drives, when necessary.

The USB 3.0 speeds are fast and external USB 3.0 drives will do well.

The full, internal SSD is THE ONLY way to go with the 2017, 21 inch screen model iMacs.

The Fusion drives in the 21 inch screen iMacs are tied to a low storage 24 GBs SSD and a 5400 RPM spinning hard drive.

The same 5400 spinning mechanical hard drive that comes as a base drive.

Apple STOPPED putting in 7200 RPM hard drives in the 21 inch screen models when the 2012 slim profile iMacs were introduced.

I don't have to see it it in that description, this is very old news/facts.

You're looking at a model MNE92LL/A in your link which has a Fusion drive consisting of a 32GB SSD and 1TB 7200RPM platter drive. It very well might meet your expectations when it comes to performance, however, from personal experience owning multiple Macs (one with only a platter drive, one with a Fusion drive and one with a SSD only), your Fusion drive choice will be a leap in performance over a platter drive only Mac but a SSD only Mac is a leap in performance all over again vs the Fusion drive. The difference in performance even if you're not a power user when everything is stored on an SSD only vs a SSD fused to a slower platter drive is simply amazing. (My 2014 MB Air with SSD only runs circles around my 2014 5K iMac with a Fusion drive, double the RAM and a faster processor.)

Hope this helps...

I must have been in a temporary fog or something.

The 27 inch screen iMacs DO have fusion drives paired to 7200 RPM SSDs.

I do not know what happened.

Maybe I mixed up posts because as of today there were 3 or 4 posts about the 21 inch screen iMacs.

The iMac you linked to should be fine, but I am still with babowa about prefering the full SSD over the fusion drives, but at least you are getting a Fusion drive with a 7200 RPM hard drive.

Again, my bad.

Fully agree.. while a Fusion drive is huge leaps over a platter drive, a SSD only is another huge leap over a Fusion drive.

All of my future Mac purchases will have SSD only based on real world testing and ongoing price reductions for this type of storage.