My Explosives skill is at 60 with frag 'nades doing 90 DAM..

should I get the perk where your explosives do 20% more damage or should I just add more skill points to explosives on this next level..

main question is, how many x amount of skill points are equivalent to x amount of explosives damage?

I usually have always just brought explosives up to 100 and got the +20% perks to fill up spots.. but on this run, I'm being as frugal as possible...

why do you want to be frugal? So you can die more often? Pure explosives barely has any perks that associate with it, so if you tried to shove as many perks/points into them, you would still have a huge assload of perks and points to deal with.