Forge version: 14.23.4.2712
Twilight Forest version: 3.7.424

So I was profiling my server (I ran the sampler for 20 seconds) during a laggy period while one of my players was in the Twilight Forest exploring with the magic map in hand and I found the following result:

Perhaps this could be fixed by running the biome generator for the magic map on a separate thread or by caching the results if they aren't already?

This has been partially addressed by 1d6c77c (build 518 here).

If this is still a problem, I'll look again at caching biome ID lookups and anything else that can be done.