Router recommendations for flattening Slabs

What you have read is excellent advice. I use a Freud FT2200 which is out of production...I think. An excellent alternative would be the Makita RP 2301FC 3-1/4 HP plunge router with variable speed.
I like the straight sided base. Of course, a straight base could be made for a round stock base as on the PC 7518. But, IMO that beast is too heavy for the job. I have one under a table where it's better suited.

Welcome to the forum. A plunge base should be used for convenience of depth adjustments as you go from all I've gathered on the subject and speed control is a must but most have that already. Here is a speed chart that gives you the suggested speeds for different sized bits. Also keep in mind that multiple shallow passes are safer then trying to deep on the cuts. I limit mine to no more then 3/16-1/4". You large sized slabs make me wonder how you can comfortably do 66" wide without moving from one side of the slab to the other considering reach unless you have a mechanical way to move the sled from front to back. Would be interested in what you come up with.

Welcome to the forum

Welcome. There are many routers that will do the job well. Anything 2.5 hp and up will do, just don't try to cut too much at once. I would never go more than 1/8th per pass with something like a Bosch 1617, but it meets all your requirements. Almost all of the name brand 3+ HP routers are top heavy. So I suggest you stick with the 1617 and make a few more passes.

I love my Triton under the table, but it's too tippy and top heavy for me to manage freehand, even with a guide. If your sled uses metal rods a really heavy router may distort the rods, tilting it will dig into the slab. A lighter router is less likely to do this.

A 1.5 router will work as well...

Welcome to the forum.

Variable speed is a must, as you'll want to use a bit similar to an Amana RC-2555.

You only want to spin it at 12,000-14,000 rpm.
You don't need micro adjustment imo, as you'll be removing a fair amount of material with each pass.

You'll need a pretty substantial fixture to span 6 ft without sagging a lot, if you want truly "flat" slabs.

at my house in Jakarta, I have this Freud FT2200. this very recommended

The FT2200 is my choice, as well.

Welcome to the forum @gunturhakim