My only advice is, on a 5/2 split, open Rebuild/Estate, trashing your Hovel. In the mirror, you normally want to be buying Duchies directly anyway, and your opponent also doesn't have them, so the lack of starting Estates isn't much of a concern. In the non-mirror, your opponent isn't playing Rebuild, so you just win a turn or two later than you would have otherwise. (If you don't win, congratulations, you probably played a board where Rebuild wasn't dominant, but commiserations, you didn't realise it).