Here's my advise, and this comes from having spent over 25 years in the business...
A) First thing is to figure exactly what you want. If you want an 850GSA, don't settle for a 750GS. Otherwise you will spend all your time thinking about the GSA and it will effect your enjoyment. Of course, if you are happy with either, great. But figure that out first.
B) Then figure out exactly what you can afford. If you're paying cash then figure out your top dollar is and don't go over it. If it's payments, then figure out your max. And always include insurance (get a quote), and leave enough room for enjoying your new bike. No fun having a hotdog when you can't afford the mustard.
C) Then start looking on the internet. Get an idea of how much they are selling for, that will tell you a lot and if you are even in the ball park.
D) Do Not Trade In! If at all possible, sell your current bike yourself. Trade-ins always complicate a deal and make it easier for the dealer to confuse the whole thing. Plus you will make a lot more than you would if you traded. Then use that for your down payment or to buy farkles for the new bike. If you do have to trade, then prepare yourself. Look it up and know what your bike is worth on a trade in value, not retail as you will be disappointed. But prepare yourself, so that you don't get screwed.
E) Get preapproved for a loan from your bank. Then you know exactly what it will cost you. Now, that doesn't mean if they can get a better rate not to take it, but you will get the straight scoop from your bank, where the dealer is looking to make a point or three.
F) Go in as a cash buyer. They don't need to know your finances, and if you are preapproved from your bank, then in essence you are a cash buyer.
G) Don't settle (see A above) and don't force it. If you really want a 1250GSA, but all you can afford is a 310, then wait.
Now here is probably the best piece of advise I can offer.
H) Make a deal that makes YOU happy. No matter what there will always be deals and there will always be a better deal out there... So, make a deal that you are happy with, then stop thinking about it, buy and and enjoy the ride.
Buyers remorse comes from one of two things in most cases. Overspending your budget or settling for less than what you wanted.
Bottom line, preparation is the key!
Just my .02
Good luck and have fun!