When picking up a brand new car these days, is it necessary to keep the engine below a certain number of revs, or keep below a certain speed, up until x amount of KMs, or is the modern day engine "ready to roll" from day one?

Not like the old days they are pretty much run in from day one now.. Oil technology has a lot to do with that too but it wouldn't hurt to give it a short period of run in time especially for the brakes more so then the engine, new pads new rotors need to be bedded somewhat before running hard or will definitely warp or glaze a rotor/rotors and set of pads mostly do to cost cutting, cheaper metals on many models.

As said modern motors are a far cry from the old ones. They come pretty much sorted. With modern metals and alloys for the engines and the new lubricants they will last a very long time as long as you change the oil and fluids regularly. Just drive it normally and change the oil and filter at 1000km as any rough edges will be rubbed off in the first 1000kms

In the past engines had cast iron piston rings that had to ''bed'' in with the cross hatch hone of the bores, that's why speed limits and early oil change were mandatory but now with chrome moly, ceramic and other typres of rings together with cylinder wall technology such as silicone impregnation stuff has really changed BUT being old school l would run an engine in carefully and change oil and filter at 1000km to make me feel happy and am sure helps the engine live a long life. Other than that just drive it.

Thanks for all the replies. Most helpful. By the sounds of it, don't go crazy, but needn't drive like a Schumacher - by that i mean slowly.

Only joking all you Schumacher fans!

modern engines with catalyzer should avoid leanburn initial 1000km. bikes and cars. leanburn appears when cat is dirty, and provides less fuel to burn. it appears when steady throttle and speed, so the break in advice is to full throttle for 2 seconds at least every 3 minutes if constant speed is required, like on highways

try to be easy on the brakes for a few hundred clicks

except for that, just like any car