If i was you id go with the f4.6 fitted to an xl,

the force 28 has enough power to push the savage around easily,

a picco 28 will be a bit of an animal compared to the f4.6 in every aspect,

more power, higher fuel consumption and seem to need tuned every time the wind changes direction,

i had a couple piccos and they ran great for me and are power houses,

but i have also have an ofna force 28 engine which runs perfect and produces hassle free tuning every time i run it,