Chosen Solution
Upgraded to a new Samsung Evo 860 250GB SSD on my 15” Mid 2010 MacBook Pro. Fresh installed Catalina through the patcher. Boot up and performance is comparable to the HDD I replaced it with. Read something about the hard drive cables. Does the original hard drive cable that came with this model of MacBook Pro only do SATA II speeds? I’m not sure what the problem is.
Not surprising! You are pushing a system which is just too old to run MacOS Catalina! The system only has a SATA II (3.0 Gb/s) SATA port and as you are forced to use APFS file system which really has serious problems running on SATA drives as the TX/RX queue depth is only two! Unlike PCIe/NVMe drives which have four per lane per TX/RX pair so a x2 drive would have eight Queue’s and a x4 drive would have sixteen! I just don’t recommend running High Sierra or newer on any SATA based system. There is nothing you can do to improve this. The next issue is RAM you really need at least 8 GB and if you are trying to do anything heavy you really need 16 GB, but thats not possible for this system. Best to go back to Sierra with GUID with Journaled file system (HFS+) which will run a lot smoother!
