I just bought a 5/4/3 SG5 for this season. Super stretchy and really well constructed, good seam placement and seals. The SGX Xero is their top of the line suit, step up from the SG5. Looks sick, I think any top of the line suits from the main brands are going to be good.
I am trying to stay below $500 so I thought about the flashbomb but I don't think I will buy another Rip Curl product. I have owned 3 different suits of theirs and they have all fallen apart (and I really take care of my suits too)
The fact that the SGX Xero is supossed to be lightweight and quick to dry is appealing...but I don't know much about how they hold up or how warm and dry they are when it really gets cold.
I have the 3/2 and it's a great quality suit. Extemely flexible and very warm so i'm sure you'd be pleased with the 5/4. Cant really help you with the hood. I wear my 3/2 all winter and put a hooded vest underneath on the coldest days. Temps here dont compare to yours but I cant think of anything bad to say about my Xero. Best suit ive ever owned.