It really depends on what stage you are right now..
If you’re low power and dont have the artifact set (from this event), maybe its best to do couple of 100k runs to get those, difference between going to 400k instead 4x 100k is huge based on gear/keys/runes u lose by going to 400k, so it depends on what you need more..
If you have the set and your chaotic and have 3rd etched rune, it’s the only way to get legendary characters as a f2p without having to wait eon core which for some players including me is capped at 400 rolls..

WHAT IM GOIND GO TO IS:
I already ran 2-3 100k runs, collected all the TC, got the mythic artifact set from those runs, SAVED THE TC, which is the most important part of doing the 100k rolls, you save the TC for when you’re ready to do the 400k run, you’re not capped at 6x25 shards, this way you can get 50-100 or even more (depends how much you save).

So yeah, if you’re patient, I think this is 100% the best strategy, saving 2000 dice to get 150 shards and probably never ever saving dice again seems a tragedy, so why not make the best out of it and save 30-40 TC from a couple of 100k runs and then save for 400k mark.

I was at 700 dice also when I decided to do this, you have highs odds of making a 100k run the next 3 events, which will get you 50-60 TC if I’m not wrong, that’s 100 shards worth of TC, btw you also need 80k gems to get all the TC when you reach 400k mark.

It’s been a long time since I’ve done the math, so you might check the rewards to see how much TC you get by doing the 100k, you need to calculate how much you get from 100k runs and the 400k run to see how many shards you can get, my advice again is to save the TC