I'm not entirely sure of the load applied energistics causes for the computer, however just thinking of it now, You're also hosting the server on that computer yes?
Did your lag correlate with something else, for example a modpack update.
It may not be client side which is causing the lag for your computer.
Indeed I am hosting. However, it doesn't get worse if people log on. I could have up to 4 people all doing random stuff in completely different areas or worlds and it's still the same frame rate (one of the first things I checked).
The problem started mainly several days after direwolf20 updated (I believe), later on I moved to Ultimate (since I started to like Gregtech despite half of my friends saying "noooo not gregtech!"). That makes me think it's not modpack update related, but I've been wrong before.
Odd question, but it could be the source of your problem. I know I helped a few people on the FTB sub reddit this way.
How much memory have you allocated for the server and the client? How many players are on the server at max?
Client should never ever need to go above 2 gigs, and 1 is enough for just about anything other than 128x or higher texture packs. The server should have between 512mb and 1 gig per client.
Just checked and the server has 4GB as well. So going by your estimates I should have plenty for the people on the server. I don't use texture packs (tried sphax x128, but it seemed to slow down the game even worse... probably a placebo)
I think at max, I've had about maybe 5 people online. That was when we had a new member that left the next day so generally we only peak at about 4 people online. On average, 2.
I used to have terrible framerate drops and crashes in one part of my base, it turns out it was because of microblocks. I don't touch the things any more, too much extra data
I've seen it happen to other people too. Maybe it's that?
I'm 100% with you in terms of not using microblocks! I mainly just absolutely hate going and rebuilding something after using microblocks. It's way too much work to go and fix things up after using them. I will, however, use microblocks if I use Blutricity (which is very rare for me)
***EDIT***
I would like to point out that if I have fancy graphics and smooth lighting turned off along with short render distance my FPS peaks at 25 and averages about 23 (still in the laggy zone)