Thanks guys for nice discussion and replying… 
So lets continue… If we compare Lead free solder Led4Power recommended to this table [Reference] Physical and Mechanical Properties of Solder Alloys we will see that Sn95.5Ag3.8Cu0.7 (which is the most similar by properties to Sn95Ag4Cu1 Led4Power recommended has highest “Tensile strength at breaking” at 600 kgf/cm² and better thermal conductivity at 60 W/m⋅K but it has low Tensile Elongation at Break of 16% while classic Sn60Pb40 has 40% if mentioned elongation at break is important for our hobby?
So I will have to try mentioned Sn95Ag4Cu1 and decide… Silver and copper in Soldering alloy can’t be bad right?
But question is can we use Sn95Ag4Cu1 as a “repair component” over lets say Sn60Pb40? I am sure there will be no problem for scratch builds but how it would behave if we merge it with leaded solder? Cause I’m sure plenty of guys here fix those Cheap(and no so cheap) flashlights for their friends etc…