is there a difference in the dmg output from the explosif device if ive perked it up to 10 or to 9?

Yes. First, each level you train installs a better Install Explosive Device (there are 10 different types). Second, at level 10 you get the awesome Thermal Primer which does an enourmous (up to 12k) nuke if timed correctly.

I really rate this as viable for even pistol engi's, your only other alternative is the Power Up perkline, and though i haven't tested it in PVP, i tested it PVM against a OA shopkeeper and all the perks in the line failed to hit with 2400 AR

it failed because your Power Up perkline attacks use Ranged Energy not Attack Rating.
With higher Ranged Energy skill you might have landed some but still not worth it for pvp