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I wasn't aware of this conversion kit until just now. It's a good idea, but I haven't tried it or seen it in person to be able to offer much advice as to how it works. Generally, I wouldn't recommend oversized bars with IHC as people usually try to do this with multiple shims, which creates instability. This conversion kit may work, but I'd be skeptical until I see it working in person.
There's not really a best compression as they are different and do different things. I can tell you this, however: ICS is my least favorite. I like IHC, HIC, and SCS for different reasons, but ICS is junk. It works okay, but it's hard to adjust and you can only use certain parts with it. Avoid it if you can.