Just don't forget to consider your ongoing maintenance budget. In my opinion there is a point where bigger is not always better. Bigger is also more expensive; time and money. More water means larger water changes, more salt, a larger more expensive skimmer, more lights, heating, cooling, etc..

For example, if today you had to the time, the space and money to set up a 150g 6 foot tank or a 500g 6 foot tank choosing the 500g because "bigger is always better" might not actually be better in the long term. The 500g tank is going to cost you more in time and money to maintain. This tends to be the cause of many tank shut downs.

Having said that, some people are perfectly fine maintaining larger tanks long term :-)

Agree on the 6' length.

Rather than upgrading selling the fish is another option!!! At least that is what I will be doing should the time come. The "tang" quantity in my 90 might get me hanged on some boards, despite their current short stature.

Rather than selling the tangs which is a lot more difficult to do than you realize as you really get attached to them, reward yourself for good husbandry and get a 6 footer for yourself.
It is just an extra two feet!

Tell that to my wife!

Here is a little secret that I would like to share with you.
Check out the trunk of the car she normally drives.
You may spot empty plastic bags from some of the dress/shoe stores and maybe even find a few crumpled up recent receipts for 'the new dress that you just noticed that she says she has had for a long time.'
Than tell her about the need for your fishies to have a little more room so that they can swim around so both of you could enjoy them. Tell her it is only two feet more

That only works if your wife isn't an Italian NYer... She would just tell me she will dig my grave 2 feet more...no matter what receipts I find... But I will say it was her idea for me to build my 180. Lol so I got my 6'.

So that being said it never hurts to discuss it with your better half sometimes they surprise you