If you do go with a SeaClear, I truely believe that you'll end up with as much $$ in the set-up in the long run. I dont know of a single person that has purchased a Tenacor and been unhappy with it.
I have set up reefs on the cheap (lower cost equip / not necessarily a bad thing) and would rather wait and do it right. I have moved cross country a few times in the last 10 years only to sell and part off my set-up's. Now that I am going to stay a while, I took almost a year to the day to gather the equipment that I have for my current 90. I had the tank and stand for almost 6 months before I put water in it.
If you really need something now, do a small tank and keep some LPS and musrhooms (what I did) and then started on the equipment for the larger tank.
What size tank are you looking for ? I'd definitely do a 36 or 48" length tank. More fixtures designed for these size tanks....
The only difference between most 55's 75's and 90's are in heighth. Most of them are 48" long. I have seen a 55 that was 36" long but it looked like a bathtub. Look at the supporting equipment (lights etc...) that you'll need to keep what you want. Are you going for a full "reef" set up. Large polyp stonies, mushrooms etc....? Or a Small Polyp Stony set up (more $$ here, need lots of flow and very high lighting...