Why Do Gem/Enchant Sims Take So Long?

TL;DR: Gems and enchants change DPS by a small amount so more CPU-intensive sims need to be run to find the best combination.

By default, Top Gear runs using Smart Sim which uses a multi-stage approach (all combinations are run at a low precision, losers are tossed, precision is increased, winners are run at higher precision, repeat). This tends to be very fast for gear and talent sims as these combinations tend to have more significant differences in DPS (gear/talent differences can often be 1% or much larger).

Gems and enchants tend to have a much smaller overall impact on DPS (often in the 0.1–0.5% range) so many more combinations will end up closer to the top. This results in many more combinations being run at 0.05% error margin which will require tens of thousands of iterations (lower precision often runs in hundreds or thousands).

I don’t believe there are any shortcuts around the simulation time if you want to fully sim a large number of gem/enchant combinations. Lowering the precision of the sim would result in a ton of gem/enchant options all falling with the margin of error which basically doesn’t result in an answer at all. There’s probably a “good enough” approximation technique using reforge plots which I’d like to look into in the future but I just haven’t gotten there yet (it would also require quite a bit of simulation time as well but probably less than a full gem/enchant sim).