I have A rated grd 1 upgrades on all my ships but had an acute attack of laziness and stopped there. Is grd 5 worth it?
The major advantages to upgrading this and your power plant is if you are seeking to obtain the highest jump range possible. In this case, you will be fitting a lower class module than the Max your ship can use and then using these upgrades to increase the performance of that module up to and beyond that of the top class version. (Grade 4 and 5 upgrades are essential to achieve that goal)
This will reduce your ship's weight significantly while at the same time providing you with more performance than the stock A rated max class offers.
You could of course just install the max class A version and modify that to allow for more stuff to be running at once etc. But the rewards for this approach are considerably less than getting say a 6A Grade 5 Distributor to outperform a stock 8A version.
As far as grind? I didn't find my Distributor or Power Plant upgrades that much of a grind.
One last thing I strongly advise... Bring MULTIPLE stock modules to the Engineer you will be working with first before attempting any major upgrade session.
(Buy and store them elsewhere and then TRANSPORT those to the Engineer base via Outfitting/Module Transfer & Storage) This will give you the ability to keep your better rolled upgrades by swapping in another stock module and resuming the process. In the end, you will either end up with one very high grade upgrade, or if you are lucky, several of them that can be transported back to your home system and used in other ships.
