There are special rescue saws with a 45degree down bar and carbide tipped chain for rescue that i think some builders have tried.
i think more power can give greater kickback, as well as a longer bar can. i think book says that you can get kickback from the top or bottom tip corners, top being more dangerous. This could happen in that portion of the bar touching something or getting pinched as the chain races around the curve. Left leg, forehead and left throat injuries i believe are most common for kickbacks. The throat injury is why the olde ones would carry that mirror to put the sanitary pad on, so the could see just where it was gushing from when they were alone, and cap it!! Hopefully not to kiss themselves good-bye! But, i always chain brake when starting, moving, pivoting etc. And i do start rear handled saws with the handle between my thighs or on the ground a la Stihl/ Eric Sorenson nwhen on the ground.
If you have both hands in proper position on the saw; it seems that the reach would be determined by the length of the most outstretched arm and handle placement, assuming same bar lenghts. It seems both of those (arm and handle position) would be about equal.
i agree that a rear handled saw would give more leverage against kickback, as hands are farther apart. One hand becomes the pivot (top) and the farther back the other handle, the more leverage on your side to fight kickback on the opposite end of the pivot. Top Arm should be kept straight.
One handed operation though, i think the balanced, lighter saw; that was made for the job, whose back end keeps the front end up would be safer without a doubt. Though Stihl Phil says that all saws are designed for 2 handed use. This is not just for safety but ergonomics. The weight, vibration is meant to be carried by both hands in all that stuff, so i try to minimize such motions. My understanding from him is that it more than doubles the load on the single arm. i have come to equate it with making sure a biner gate can't open, it seems that with both hands locked on the saw, that my chest carries some of the abuse and not just my arms.
Stihl 020 here, gotta go from Corona to Silky. i think i can command more precise action with the wider speed band of these higher revving chain saws, and eliminating fiber in pre cutting. i can always make it cut slower, so i set myself up for as much speed as i can with the fast saw and eliminating wood, then go at the speed i see fit as i watch for head or backcut movement while cutting.
Oh, and my lil'butt is more likely to command a lil saw totally in these conditions .
