As far as I can tell, there's no need to jump ship until the offer is declared free of all conditions (on or around the 2nd of Aug) - assuming it is so.
Advantage of doing this is that you can still accept a competing offer should one arise. If you sign over early, you are unable to sell on market or accept a competing offer.
Prima facie, I do like the GRY offer, but I'm not going to lie, I'd like a higher offer more....
SHX Price at posting:
22.0¢ Sentiment: Buy Disclosure: Held