I e experienced less growth but fairly close, started at the same size, got it to about 16-18" in around 5 months, is is feeding are sticks once a day, skipping days sometimes, and he wasn't the only fish so he didn't get all of it, he was with greedy cichlids. I believe a guy grew three up to 2' in one year, he might've power feed them though, idk. But one should assume 2" of growth each month for an aro in the right conditions. So if you plan in caring for it properly, feeding it enough and keeping up with water changes etc, that tank won't last more than a few months, as others have stated it is a very active fish and will utilize the whole tank front to back and side to side. The 220 isn't worth upgrading to because it won't last much longer and you will be out $1000+. Use the money and buy the materials to build the final home. Imo a 600g 8x4 is good for a silver aro as a final home, you may decide differently once it's in the tank however if it gets larger and with its activity. 6' and even 7' isn't enough imo. The 8' is pushing it. And 4' width is good.
So again, skip the 220 and buy the materials you need and get to building the larger tank ASAP. As said they are flexible, so though the fish won't be happy, you can get away with the tank for a little longer if necessary.