I have two 12g and one 20g Magnus Limited Fields and they are beautiful guns to shoot. The balance and fit is perfect for me. I can practise three rounds of skeet with the wood butt plate and feel no effects of recoil.
I do not have the 20/28g combo in the Magnus but I do own two Tempio Light Fields in 20g and 28g. They are both built on the 20g frame and are very close in weight. The 28g feels a bit less whippy than my 28g Rizzini Aurum Light which is built on a scaled 28g frame, but that is only noticeable when comparing them side by side.
Personally, if I were to have only one gun for the shooting I do, I would go for the Magnus Limited 20/28g combo.