Thrawn’s speed...

If you find you want to use his fracture quicker, you need more speed on him...
That's about all we can say other than generally you want him quick.

You can always aim to get good speed secondaries on tenacity mods if that is what you want to do.

I have him at 273 with mostly health mods. Would like different ones but they are my 2nd fastest mods.

If you can use his fracture sooner you could possibly eliminate the threat of debuffs. Are you in a heroic sith raid guild. You get 12 extra speed from his g12+ gear. I have speed and health sets on mine and both g12+ pieces. Have him at 302 speed so he usually goes first to fracture whoever.

And if you fracture first, his zeta gives him a lot of tenacity, so he won't get stunned while someone's fractured

You're only sacrificing 16 speed at full G12+ by not using a speed set. They aren't the be-all/end-all of mod sets.

If you can get great secondaries on your tenacity mods you should easily be able to boost him by +105 (5*15 + 30 from the arrow). You might end up with better speed than RNG will grant you by slicing/farming speed mods. And you'll have mountains of tenacity on top.

Ridiculous luck will net you a +130 5-dot set. If each secondary is +20.

Slicing to 6 and you'll be even faster.

I use Thrawn at over 300 speed. He needs to fracture as soon as possible.