Largest router bit I can use WELL

This 1 1/4" dish cutter, second shot, has had regular use in hand-held router and as has been said, there is little chance of lines between cuts compared to a bottom cleaning bit which must be set absolutely square to the work-piece.

If the material isn't flat, bowedor twisted, you'll need to prop it up in order to flatten it uniformly across the full width. You will also want to have a jig to guide the 618 router as it flattens the top. If you have a good #4 or #5 hand plane, you could shave down the high spots on the inside of any bowing to help level it so it is stable on the work surface. Stick's pictures show the router running on a pair of bars.

The two pictures show variations on simple router sleds. Note that the outside long edges have an added piece on each side to restrain and guide the router as you move it across. Once the workpiece is planed or propped up, you adjust the depth of cut by raising or lowering the bit. Go lightly in small steps until a straight edge show's it is flat on one side. If you have a planer, you can level the other side, or flip it over and use the router to cut the otherside til it's flat. You will still need to do a little sanding and scraping to have a finished surface. You'll need to buy stock somewhat thicker that your desired finished thickness.

Harry's Router Sled jig uses metal bars to keep the bit cutting level all the way across, the pictured designs use some very flat Baltic Birch ply for the guide's runners. The smaller edge guides reinforce the jig and keep it flat. The opening needs to be a little wider than the biggest bit you plan to use. The opening doesn't need to be adjustable since the outside guides need to be a close fit to the router base.

Notice that the picture with the slab shows use of wedges to level off and keep the slab from rocking.

It is flattening the second side that renders the piece parallel and usable. Note that in the second picture, the maker used aluminum "L" bars.

With the popularity of slab lumber in recent yrs the market has been taking advantage of the trend with DIYers. I got slab lumber around here like it was 2x4's.. or so it seems. Anybody with a dead tree in the back yard is having it milled into slabs and asking crazy prices....oh well,,, gonna be lots of great deals to be had in a couple years.
Unless they hear of "air dried" lumber..Yikes...

any hooooooooo... I've seen planer bits up to 3"'s in diameter..the bit itself looked kinda iffy at best. wouldn't touch it with a 6 HP router. Personally, 2"s is about the max I'd go to or be comfortable with. And the more mass the better. Infinity has a new one that fits that bill nicely at around 100.00 with a 2' cutter. Amana has a 1 1/2" carbide bit with replaceable cutters for *GULP.*.....in the 180 neighborhood. Not my neighborhood, thats for sure...*L* Whiteside has a really nice spoil board bit for around 70 bucks. (not sure if it qualifies as a cross over or not??)

Not a big fan of bowl bits only cuz by the time you take into account the radius and overlap you're probably cutting well less than 1" worth of material with a 1 1/4" bowl bit. In the end, the set up and the jig used are every bit as critical to success as the bit being used. IMHO...A 2 1/2 hp router should be plenty big enough,,, just let the router tell you how fast and how much you can get away with.

just my 2 cents worth...

As nice as your jigs are, the ski mounted router is far more versatile..