Well No It's not like the Stihl is a Toyota Prius and the Echo is a V8 but look at this way, if you use the machine the BR 600 vs the 770T it would save you enough money in fuel cost alone in one year that you could buy another 255LN. It's not always about the biggest and baddest, it should be the bottom line at the end of the year, how much money goes in your pocket.
I think your approach to this machine is all wrong. I've always said in lawn care time is money and either machine you buy the 600 or 770T could and would save you a really good amount of time everyday, enough that you could maybe add another cut at the end of the day but if your not using it, it can't pay for itself. If your going to buy this blower and us it only for fall cleanup your wasting your time and money, don't buy it. It should be your primary blower and be used on ever job you do during the day and the 255 becomes your back up.