Originally posted by Rondec Full frame is hardly expensive any more. You will pay more for top end Olympus camera than you will for a K1 or a D610. As for bulky, they are larger, but certainly NEX cameras with variable aperture lenses aren't that big. For that matter, stick a FA 31 on a K-1 and it is reasonably sized. Somehow people focus on size of a camera when combined with f2.8 zooms, which is something, but not the way you always have to shoot an ILC.
For less $$$ (as I demonstrated) you can get a full 24-300 (135 equiv.) constant 2.8 that has less weight than just FF 700/2.8 from ANY brand. That's 2 pro lenses and a pro camera with room to spare in weight and mass just against one FF zoom.
This includes body and 2 lenses. EM5 Mk ii or even a Panasonic GX 85. The EM1.2 is not cheap, but blows away the AF/FPS of the K-1 with 4k video, is 2/3 the weight, and with equivalent glass falls to 50% the volume and almost 40% the mass.
Primes barely budge that metric. In fact, an argument can be made that the extra space and mass you'd save on mirrorless allows for more primes as part of an extended kit. Both Olympus and Panasonic use this point in marketing.
Generally with top gear, you'll save 20% volume with bodies and 30% on glass, with the difference increasing with zooms to almost 40% volume adjustment, and well over 50% in favour of cropped in mass alone. And the pricing starts to favour cropped considerably, as demonstrated above (600mm lens for FF gets to $10k, but in cropped can be $2,600). And the video is starting to dramatically favour cropped sensors, at a time when video is taking off as a core feature.
Fuji's mirrorless bodies fit the small (and lighter, even) parameters, but their lenses are bulkier, but still much lighter than FF. The Fuji 50-140 is 40% lighter than the Pentax 70-200, and $200 cheaper with about 15% less volume.
Smaller, lighter tripods follow all these calls as well.
The cropped sensor, mirrorless form factors are why Panasonic, Sony, Fuji, and Olympus are doing well financially and mirrorless is picking up steam, especially in Asia. Within 3 years it will dominate all ILC sales worldwide by a considerable margin, all pretty much crop sensor. The DR/ISO whole IQ "thing" of FF has been blown up to meaning so little, not in visually measurable results for most photography, even at this multi-thousand $$$ outlays.