I am not a pilot, but I can give you an engineer's perspective of the FX2 conversion.
The Turbomeca Arriel 1D1 in the AS350B2 has a MCP rating of 625 SHP. The LTS101-700D-2 has a MCP rating of 650 SHP.
In the SD2 conversion, the FAA required Soloy to only allow the LTS101 to produce as much MCP power as the AS350B2 was originally certified with, so 625 SHP.
However, the FX2 conversion was allowed to take advantage of the full LTS101 MCP rating of 650 SHP, 4% more power. If you look at the Helilynx
350 FX2 website, on the right are links to their FX2 HOGE and HIGE charts. You will be able to see the benefit in gross weight the FX2 conversion has over the AS350B2.
Hope this helps.