Complex Vector Computations

EDIT: oops - sorry shg - didn't notice the title request

I think this will be difficult to achieve using a SUMPRODUCT (non-array entry) given the nature of the A3 calculation

You could perhaps use the following Array:

G10:
=SUM(($D$10:$D10*LOOKUP($B10-$B$10:$B10,{0,5,8},$A$1:$A$3))*IF($B10-$B$10:$B10>=8,INDEX($C$10:$C10,1+ROW($C10)-ROW($C$10))*300,1))
confirmed with CTRL + SHIFT + ENTER
copied down

The above replicates your expected results though does make assumption of whole numbers in B10:B18