Hey, man, get over the buyer's remorse. Even if you got it for half that price, you'd still be wondering if you should have gotten a different bike or whatnot. I think that's a normal psychological reaction after spending a big chunk of cash on a long coveted item.
Just think to yourself how much having the bike is worth to you? If it is worth $5400, then you got what you paid for, but if it is worth $1 million, then you got one hell of a deal!
It's a sweet looking bike, so forget about the money that's already gone, gear up, and go ride the shit out of it!