What are the dimensions of the 90? If it is a 48x18x24, I would say the Ray2 will only put you in low-low/med light. I had one on my 36x18x24 and after switching to a BML XB dutch the difference in growth is night and day.
You might be able to do a single fixture if you go BML XB unit. Their website is done well, and if you have questions, they are great to talk to with to get the right unit. If you go T5HO, you'll definitely need a quad unit if you are shooting for high light. You also need to think about the heat factor as well.