I’ve been where you are right now. Unless you are really very, very good with a Dremel or have access to CNC equipment, making scales for a Griptillian is going to be a challenge with the nested liners. Tolerances to get blade centering right are pretty critical.Ill probably buy micarta scales for the mini grip if i don't like the plastic scales. I may even make some, are there any good forum threads for making scales?
As to knife choices, you are basing your experience on a SAK and a Leek, both flat ground with very thin blade stock and are probably two of the best “slicy” value knives available. As soon as you look at larger knives with thicker blade stock and sabre grinds (Griptillians), slicing performance will suffer but the ability to perform harder cutting tasks will increase.
I had one of the old 154CM Manixs (not flat ground) and gave it away. Too much jimping on the handle and after using Axis locks, the CBBL was disappointing. I have not tried one of the LW Manixi (?).
The Griptillians (mini and regular) are great knives, I have numerous of each. Omega spring failure is not that common. I live in South Africa and Benchmade sent me spare springs. They have been in my spares box for years and never been needed. Two issues with the Grips : IMO the best blades are discontinued (Ritter and hollow ground sheep foot), the current sabre ground blades may not slice as well as you are accustomed to coming from a Leek and a SAK. The other thing is the “clacky” noise they make when closing (particularly the full size). It bugged me 10 years ago because it sounded cheap, now it doesn’t worry me as I value the other traits of the knives more than that minor irritation.
The Delica is a great knife and a best seller with good reason. Slicing performance is going to be similar to what you are used to. My issue with the handle is the pointy bits that may be uncomfortable. This is very personal - I love the blade, dislike the handle shape. I still own 5 despite that.
Of the 3 you mention, I’d take a Grip but with the understanding that it is going to be different to what you are used to ... if you can swing it, get a Benchmade Bugout, all the good features of the Grip and none of the bad. YMMV