Ger21 knows a damn sight more than I do.
As far as I've read some use a 2:1 gear reduction using 4nm steppers to get the 8nm you mention. Not reductions using 8nm steppers themselves.
I like the servo option because of the accuracy and speeds that can be achieved with the right units which is why you get a price tag with them.
The BF30 is a lot bigger and twice as heavy than a G0704 that many have so my philosophy would be to go 30% bigger than what the average user has on them.
Overall for me it's got to be option 2.
Option 3 sounds too small without a 2:1 gear reduction. The saddle & table has got to be 60kg combined or close.
As for option 1 I'm no way clued up on servos yet.
The Syil X7 is only a little bigger in size (a lot heavier tho but that's including all the kit on it).
That is fitted with 8nm motors.
The Syil X5 is G0704 size and uses 4.5nm.
So for a BF30 direct drive anything 7nm to 8nm should be near enough imo.
Either way In terms of speed I can envisage a maximum rapid of 1500 to 2000mm/min with dovetail ways.