Will twice the price give you twice the knife?
No, of course not. Down near the bottom of the scale, quality can increase dramatically with cost. The difference between a $5 and $20 knife can be incredible. Between $20 and $40 can be substantial. Once you are up in the $50-100 range, the quality curve starts to flatten out. Extra dollars don't buy as much of a quality increase. As you keep pushing up, you can still get better quality but you also get deeper into the curve of diminishing returns. Ask yourself by what percentage that M4 Freek would better serve your needs. Is it worth twice the price?
To put it another way, forget about the Freek for a minute. Just looking at the knife you have, do you love it? Will it serve your needs? Let's say you bought a back-up in case something ever happened to it. Would you be better or worse off than if you had just bought the Freek with that same money?