I like the wider beam on the Gulfstream - the feels much bigger than its listed length. I have a Sailfish my friend has a Gulfstream. He loves the Gulfstream and beats the crap out of it. His only complaint is the he feels underpowered with a 250 Yamaha 2-stroke on it.
I'm a used boat buyer so I can't help with dealer markup - I suspect there are a lot of variables. That might be a good question to post on THT on a busy night.