Purple T3s generally max out around 17k HP and 2K ATK/Mag and roughly 1.5K MR/DEF/Spec - depending upon what specific stats are there.
For Example...
Purple T3 Maxed -- This is the current event T3 purchasable with TT frags I just grabbed this
Future Augment
17.9K HP / 1800 ATK / 1200 Special
If you have the same color and T level in another Cosmic you can get a feel by looking at those. There's some minor variations but not a great deal. These stats are very close to other Purple T3s I have give or take a couple hundred in stats.