Breathers - the reason V-twins (and big singles, 360deg parallel twins, boxers etc) are significantly different to multi-cyl engines is that the piston motion means that the crankcase volume is cycling up and down greatly as the engine rotates. A 4-cyl inline engine "exchanges" gas between cylinders going up and those going down, as do other multi cyl arrangements (more or less).
This means that there is a lot of bulk flow and reversal in the breather pipes in addition to the actual blowby, which can tend to carry more oil mist. There also tends to be high pressure reversals in the crankcase, which can give more joint leaking problems than in an L-4.
However, oil consumption associated specifically with high speed+load is usually piston ring and bore geometry issues (generally termed "piston/liner interface). Particularly with the short slipper type pistons as in most modern bikes, the piston attitude (tilt) control becomes more tricky, and this can lead to ring lift off from the bore surface, or ring "flutter" in the grooves, which will dramatically (in relative terms) increase oil film thickness and thus oil consumption.
True "ring-flutter" is usually at high speed when you remove all the load (overrun or gear changes) and the gas pressure between the various rings causes the top and second rings to vibrate in the grooves, which drops the gas sealing and allows oil to get round the back of the rings. You often see a little puff of blue smoke when this happens.
Ring design is like most things a compromise of weight, dynamics, wear, friction and cost. The weight issue is a lot bigger than first sight suggests - one mm on the piston crown (ring pack) height means an extra mm on the height of the whole engine.
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