a 5k machine comes out to:
subtract 138lbs per inch at a 36" center and 104 lbs per inch at 48 inches (2500 reduced cap)
so thats "close" but not entirely accurate
(subtract 3333 from 5k =1667 less lbs. divide that by load center diff 1667lbs / 12" = 138 lbs per in)
but as u go up in capacity that "guesstamation" would be less accurate and possibly dangerous

i serviced a factory with 11000 lbd mitsus with 60" capacity paper roll clamps
the clamps could handle a load center of 30" and added about 4" to that from the face of the forks
that gave them a load cap of about 7765 lbs (actual #s were prob a lil different but this is close)
that makes a difference of 323 lbs per inch at a 34" load center
at 36 it would be 306 per inch less
and 229lbs per inch at 48 (if it had forks lol)
with your estimation the 11000 lbd machine would have a new capacity of 10000 lbs ( at 34") more than 2000 lbs more than the actual reduced cap which would be very dangerous

and now u know how to do the calculation you wont have to guess lol