When I bought mine, my dealer led me on a real song and dance regarding the cashback thing... changing up the deal on me more than once, including as I was about to take the keys from them. I actually walked back out of the dealership, past the bike that I thought I was about to buy, and out onto the street before they ran after me and relented
So, here's what I would advise... leave the cashback out of the equation as the dealer will only use it to try to trick you - "oh, no, that price INCLUDES the cashback, didn't I say?" etc.
The way it should work is that you agree a price for the bike, shake on it, and that's the price you pay. Then at some point (took my dealer weeks to do it), the dealership writes you a cheque for the cashback, which they will claim back from Suzuki.
Say you agree on £6,000 for the bike hypothetically, get them to put in writing to you that the price for the bike is £6,000, plus you will also receive £800 cashback as well.
I'm not sure what the price of a new Glee (forum speak for new V-Strom 650) should be, but that sounds high to me. There are usually good discounts to be had on Suzukis if you haggle enough I hear. I would call around a few other dealers and see what they can offer.