VFC HK417D hop units

[Viggsy]

Looking for advice on what hop unit and barrel to upgrade too, was thinking madbull ultimate plus a madbull ultimate 6.01 barrel to replace the 6.03. It has a VFC rotary unit in, how good are they and is it worth upgrading.
Also should I go H Hop, Flat Hop or R hop.
It appears to be slightly under powered as well. Any advice on stronger springs. It has the reinforced gearbox in.
Will be doing mosfet and wiring, any ideas
Also any other ideas on

Cheers