How is the 5.6 to 5.8 migration process

Hi- I have been putting off migrating a very large 5.6 site to 5.8. The site includes a lot of custom blocks and a ton of pages/content/images. Has anyone migrated a site with custom blocks? Assuming I successfully recoding the blocks in 5.8 -- does the migration tool do a good job with moving the pages including custom blocks?
Is there a good sources that summarizes the differences between creating a custom block in 5.6 vs 5.8? Any good examples showing what a contoller.php file looked like in 5.6 and how it was changed to work in 5.8? Any suggests for removing some of the pain from this process is greatly appreciated.

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ConcreteOwl replied on at Permalink Reply
Are you moving to Version 8 because of a server php upgrade?
If that is your only reason, why not upgrade your 5.6 site to run on php 7?
I have several 5.6 sites running on php 7.3 without issue, and very fast since the 5.6 code base is super lightweight and very stable.