from what I understand, the mahle pistons are not forged, but its been translated into forged from their manufacturing process (which may be pressure die cast, not that I know for sure)
Pistons are fine but rods need changing arguably these days... its subjective at best as stage 1 levels of tune have been known to bend rods... essentially though if changing to larger turbo (hybrid or BT) then fit rods... if you have a sound bottom end with decent bores then std pistons are fine up to around the 400hp mark... if needing to replace the pistons for an oversize bore though then use JE's or similar... if heading above 400hp then valves and springs too... large port head helps on BT and indeed hybrids...