USB3.0 SSD or internal SATA SSD?

I’m trying to upgrade my late 2013 iMac (non fusion) from a mechanical HDD to SSD.

I have a Crucial MX500 SSD, now I’m wondering if it’s going to make a significant connecting this SSD as and internal one with SATA interface or will it not be that much a difference if I use a good USB 3.0 enclosure and boot off the SSD as an external one?

Did a speed test on BlackMagic for the Crucial MX500. These seems to be orders greater than the mechanical HDD that came along with the iMac.

But the big question is, will I get better speeds if I use it internally with the SATA connect?

The verdict is out! My 1 TB Crucial MX 500 SSD connected to the internal SATA 3 interface is faster than the external USB 3.0 enclosure. Below is the speed test in Blackmagic before and after I attached the internal SSD.

Before:

After:

My biggest concern was whether it was really worth the trouble of opening up an iMac myself just to get a minor (or maybe no) difference in speed. But looking at the result I am definitely satisfied.

While I had opened it up I thought I might as well change the RAM modules, so I got a Kingston 16 GB (2x8GB) SO-DIMM kit and fit it into my Mac. My Mac is simply blazing now. I am so happy with the results. I normally run Machine Learning algorithms on my machine and some processes like the k-fold cross validation takes about 20 mins, but now it is hardly a minute.

Some pics of my PC Internals:

Did a speed test on BlackMagic for the Crucial MX500 (see below my update as a reply). These seems to be orders greater than the mechanical HDD that came along with the iMac.

But the big question is, will I get better speeds if I use it internally with the SATA connect?