After just reading up a bunch about these here is some info i found:
Here is a great detailed article comparing all the cleaning robots out there. It recommends the Roomba 650.
The best robot vacuum for most people is the $400 iRobot Roomba 650. It’s easy to use, works on bare floors and carpets alike, and leaves out the unnecessary features that drive up the price on most bots.
Second place was the more expensive, but not top of the range Roomba 760.
I strongly considered including the Roomba 760 as a semifinalist, but decided against it. It’s one step up from the 650, only costs an extra $50, and has some features that looked like they might’ve been useful—particularly the Persistent Pass, which will allegedly spend more time cleaning areas that are extra-dirty. I couldn’t find any solid evidence that this is actually useful, though. My hunch is that, since bots aren’t especially great cleaners anyway, it’s like spending time trying to break ice with a snow shovel—it’ll get the job done eventually, but you should just use the right tool (an icebreaker) instead. It also has a remote control, which could be useful, and an extra virtual wall. The dust bin can hold slightly more dirt, too, because it uses a smaller filter than the 600 series. It’s not a bad bot at all, but I don’t think there’s anything here that really makes it a better buy. (The previous Sweethome guide to robot vacs suggested that it might be better for pet owners because of the HEPA filter, but that just didn’t turn out to be true.)
The rest of the 700 series (770, 780, and the now-discontinued 790) are what Cangeloso calls “luxury” robots. Each successive model adds one or two extra features, like a full-bin indicator for the 770, and touch-sensitive controls for the 780, that do nothing to change the cleaning ability. Each tier costs $100 more than the one before it, which isn’t worth it.
Costco has its own Roomba 655 which is selling for $349. Aside from being grey and not black it looks exactly the same as the 650. It has some advantages over the 650, it includes a "iRobot XLife Extended Life Battery" which is the newest battery and delivers twice as many cleaning cycles which only comes in the 800 models, plus it includes some bonus brushes and cleaning tools not included with the 650.
Or BB&B has the $650 for $399, may try to match to amazon $360 and then use a 20% coupon. YMMV
