Agree with Karen - rules of thumb are just that - they are not formulas, and just as you can get two children from the same family one chubby and one like a rake, it is not only different breeds but individual pigs that vary.
We do pure saddlebacks, and GOS, and crossed everything else, from Kune kune, LB, OSB, LW, Berkshire, even mangalitza !. We go to on a lb a day per month up to six months, so ours get a max of 6lbs but we feed everything on sow food (bulk purchase make this cheaper) , as we only do a few meat pigs for family and friends so are not "speed finishing". You may well need to feed less if on growers.
However we also adjust on
time of year, less in summer, and more in winter,
Sows vs. meat pigs esp last stages of pregnant
Adjust for fresh veg or good pasture
We tend to feed less to GOS - who seem to run to fat given any chance
and our jugs do 3lbs, so we are pretty good on getting the quantities right - ie not generous portions
Feeling your pigs as per Karen regularly is the best way to judge condition, you cannot do it from eye alone unless you're at the extremes !