a 90 to a 125 isnt really a big jump anyways IMO. Scape wise the rockwall probably gives you the most base room for small corals but really without a much bigger upgrade (including front to back upgrade) you really don't gain alot of extra space, especially when you space out larger corals that grow faster then smaller ones. Even going from a 125 to say a 180 probably wont give you the significant increase in room you are looking for.... may I suggest a 6-8'x 30-36" front to back tank.... that should suffice for a while lol
Or your other option is to weed through the corals that you only somewhat like and create more space that way... or have a big frag party and frag it all down and watch it grow back in again while creating more space for a while atleast.