Any locals like me with reasonable bargaining skills (well haven't lived there for around 10+ years but I do still speak the language and go back often) can walk out from an AD with 25-30% off RRP easy, however 35-40% is also common nowadays because
1. there are nearly 2 ADs that carries breitling, rolex, omega, IWC and other high end watches etc on every street so competition is very high
2. Hong Kong is a free port so therefore no import nor export tax that's why the ADs there are willing to give higher than usual discounts
3. Breitling isn't as popular over there comparing to the US, Japan and Singapore. Honkers normally go for Rolex, IWC and Sinn (don't ask me why). Therefore an AD will be very happy if you walk in an enquire about a Breitling
but bear in mind that they would probably be reluntant to give you that big a discount since you're a tourist .they try their very best to rip tourist off. so if I were you I would try not to look like a tourist at all because they are heaps of expats overthere and I don't think they would be able to tell whether you're one or not. So don't walk in with a map or camera in your hand =)
Be firm and if they're not willing to give you what you want just tell them you'll go next door and walk out . Chances are they will immediately offer you different deals or discounts. (Normal bargaining skills of course)
and yes don't forget to get the AD stamp on your warranty card

I have yet to purchase a Breitling from honker but I will try to find out which AD's the best and would most probably offer the best deals
Do go to the ones in Central (HK island) and Tsim Sha Tsui (Kowloon)... there are heaps located over in those 2 districts and are usually the most reputable

there's around 8 ADs alone located on Nathan Road in Tsim Sha Tsui, Kowloon. so you'll have a lot of choices
and by searching on breitling's website there's a total of 22 registered AD in HongKong. That's heaps consider how small HKG is..Brisbane only has 2 ADs here grrr
Carrie