I started with a used S3XL and regularly wanted to cut bigger things. So I bought the expansion kit (no longer available) from Carbide 3D to convert it to an XXL but I combined the XL and XXL rails to make a machine bigger than an XXL. Linked here Shapeoko 3 XL + XXL Progress. I did this only for size. At the time I don’t think Carbide 3D offered anything larger than an XXL. I mentioned this modification only because I probably lost rigidity which would be detrimental to my cut quality especially in metal. The only other modification was to upgrade to a Z plus. This was because I saw problems (lost steps) when plunging into aluminum with the stock Z. The Z plus helps but it is not a cure all. (Probably need ramping toolpaths.) I am very happy with the overall machine and Z plus but I don’t expect it to be a home replacement for a $100,000 machine.