The best arm/straddle angles, pad toe, cables etc are not going to give you great braking if the cable stops are bendy. There are plenty of bendy fork mounted stops, but very few that are properly up to the job.
The easiest to get hold of is the old Kona cast item and i think Dia Compe might have made a chunky item but not seen one in the wild. The difference in lever feel between the chunky Kona stop and the lightweight bendy things is night and day.
For the rear, if there isn't a cable stop attached to the frame, is to attach one. If you have a monostay get one of the rivet on type, off a broken Ridley CX frame for example, weld one on, or get in touch with a chap on ebay who has the username, alexbigtimebill . He had a load of repro Cannondale H-pipe stops machined up and they are very nice.
They are meant to be mounted on to a seatstay bridge so i filed a radius into the back of the H-pipe, so it would sit better on the monostay, I then drilled a hole through the monostay and Bob might be your uncle. Of course they will work if there is a bridge on a non-monostay frame and could work at the front if spaced off the fork to clear the lower headset.
Of course; the best at the rear is getting a stop welded on at the right height.
Another thing that can let the side down is how ' in line ' the cables are, at the braking end. Look side on and idealy the inner cable, that comes out of the stop, should not go forwards or backwards. The straddle cable mounting points on the arms, the straddle, and the inner should be in a nice straight line.
For my forks (Stephens Ritchey Logic lookalike) i had to file a good bit off the back of the Kona stop to achieve this with M900's. The H-pipe repro gave a super straight line with M900's on the back of an '98 Orange O2 which was pure luck.
i have tried some different seatpost clamp mounted stops that hang of the bolt but they were shite. Solid mounting is the way to go and makes a big difference.
Top tip for M900 fans, to improve rear braking, is to try and get hold of another front set to replace the shorter rear arms, or get the M900's that had equal length front and rear arms. I am pretty sure the latter are two pairs of the longer arms.
Another top tip for M900's is to check the wee little thread in the arm that has the centralizing grub screw. Take all the bits out of the arm and put the grub screw in, with some coppa slip, and screw it in and make sure it goes all the way through into the bore of the arm. You might have to do a little back and forth with the screw to do this.
I say this because you might be pulling your hair out wondering why the arms will not centralise even when the screw appears to be screwed in. The screws jam before doing their job enough, and It will be the last few threads that need cleaning out that will allow the screw to push against the plate in the arm, and in turn balance the arms. This could also happen in other arms than the M900 that have these tiny grub screw threads. A tap would be pro but i found lubricated grub scews and taking it a bit at a time clears the threads out without binding.
Another killer for canti performance is canti post wear, or worn arm bushes/bores as Toe in will instantly become toe out with floppy arms.