Heph reported when running alongside Gregtech, the Content Handler goes haywire and takes an extremely large amount of CPU time to load. I'm not sure what causes it, but we've got some screens and logs - note that Binnie's Extra Bees mod seems to have the same issue we do - I have logs of the actual problem, but they are too large to post here, or in pastebin. I've got local copies I can provide if needed. Here's a brief description of Binnie's Mods having what appears to be a similar problem:
https://bitbucket.org/binnie567/binnie-mods/issue/32/startuptimes-in-conjuction-with-gregtech5

Without Reliquary:

Libsandstone going buck-wild:

In addition to the issues above, there's been a report that the content handler may be initializing items or blocks too late in the lifecycle of the mod. Forum post references this crash.. note that there's absolutely no evidence this is caused by Reliquary. We really need more supporting info to confirm this is an issue on our end, but it might be worth looking at: http://pastebin.com/kwt9cx1H

After more digging and discussion, it appears Gregtech is majorly responsible for this issue, for scraping the ore dictionary and recipe lists. Whatever it's doing, it's causing our Content Handler to call a relatively lightweight method way more often than intended. Either Gregtech can implement a hack to get around this, or improve whatever algorithm is hammering that method - outside the context of Gregtech, there's very close to nothing we can do about this. There is still the possibility this is a lifecycle issue. I'd suggest bringing it to Gregtech to see what is recommended.

1. I asked Heph to come on IRC and try a few things for us, but without Gregtech we have a fairly small CPU footprint. If nothing comes out of our testing, it'll simply be an issue out of our control.
2. Shouldn't be possible. While checking items, let's make sure all the recipes work too, just to be safe. But I'm going to let this one slide.