Been running a server for a while with Mekanism, and started having some MASSIVE tick problems after upgrading to 4x ores.
After narrowing down the problem to Mekanism and testing for a while we finally found out today that the problem seems to be the Chemical Infuser!
If the tanks on the Chemical Infuser all gets filled up it starts using a LOT of tick time, upwards of 100ms Mean Tick Time total, instead of the normal (for our server) around 20ms Mean Tick Time.
It seems that the longer the CI stands around with filled tanks, the longer it takes to tick it.

For a full list of the mods that we use you can go to: http://ibkicraft.dk/modversions.php
We also have http://www.curse.com/mc-mods/minecraft/forgeservertools installed for the /tps command...
If needed i will try to make a screendump of a couple of /tps commands over time, showing the slow increase in tick-time..

Mind providing Opis/VisualVM reads?

I cannot give you Opis reads, since we can't get it to work on our 1.7.10 server :S
I'll try getting VisualVM running again.. what reads do you want from it?

(also have to get the CI filled again to get you any kinds of reads)

two screenshots of the tps.. one is after having had the server running for a good while... the other is right after restarting it...
https://dl.dropboxusercontent.com/u/17212080/Sk%C3%A6rmbillede%202014-08-21%20kl.%2022.21.04.png
https://dl.dropboxusercontent.com/u/17212080/Sk%C3%A6rmbillede%202014-08-21%20kl.%2022.23.40.png

I tried VisualVM, but it totally kills the computer we have the server running on when i start profiling :S
So i won't be able to do much until Opis is updated for 1.7.10...

What exactly makes you think that it's the Chemical Infuser that is causing your tick time? A single tile entity should really not be taking up any more than 30 microseconds, much less 100 ms.

Update: it now happened without us having a CI connected.... but it IS Menanism related........
tps dropped after we had destructed our Salination plant, removed our two power cubes, and cleared out some inventory in an Advanced Factory (Purification)....
I will get back when we have tested some more!!

Well... it is related to the Chemical Infuser anyway... the tick time only starts rising when the CI has it's "output" filled with Hydrogen Cloride, and attached pipes are full as well...
If we stick a gas tank into it and the output empties out, the tick time goes down again.
It may not be the CI itself, it could be pipes, power or something else connected to it....

I will try to create the setup in a single player map some time during this weekend to see if i can reproduce it outside our server...

Okay. Considering this is a broad "slow ticking" issue, I am going to close it. I have already done a ton of performance boosts for v8 that should make some mechanics work 80 times faster!

look at logistical sorter

I up your closing of this issue and supply you with screenshots of Opis (now working on 1.7.10)
Chemical Injection Chamber is the culprit! (at least right now)
https://dl.dropboxusercontent.com/u/17212080/Mekanism%20-%20Chemical%20Injection%20Chamber.png

https://dl.dropboxusercontent.com/u/17212080/Mekanism%20-%20tick%20time.png

Just noticed:
We have a gas tank (item) in it... with Hydrogen Chloride.. pulling it out drops the tps back down to normal... putting it in immediately raises the tps...