People mistakenly think the A900 is just a slightly larger version of the A700 with a LARGER viewfinder and 235% LARGER sensor size. The real fact is that a 35mm Full-frame is a whole different format (even though you can interchangeably use the lenses between the formats) and gives a completely different feel from an APS-C crop product. When it uses the entire 35mm imaging circle (when compared to using just a small cropped portion of it, like the APS-C crop products) its lenses perform differently, and when framed the same, it provides a totally different effect than an APS-C crop product and a variety of other factors that changes the way you photograph.
Bottomline, this is not the decision between an A100 (consumer-grade APS-C) vs an A700 (semi-pro APS-C). This is a lot more involving decision, that could change the whole nature of your lens portfolio.
I personally will move to the A900 as soon as I can. But whether you want to go there is completely upto you....it could be highly rewarding but it won't be cheap. My Canon friends who moved from the Canon 30D (APS-C) to the 5D (Full-frame), simply could not go back to shooting with crop bodies - but again, that is a very personal decision.
The A900 leapfrogs over its cheaper competitors like the 5D, by providing a 100% viewfinder that is larger than ANY other dSLR EVER, other than the $8000 1DSMKIII. Providing a 100% Full-frame viewfinder is a whole dimension different than a 95% or 97% viewfinder, since the manufacturing tolerances needed for 100% is a class apart. Also, body-based Anti-shake in a Full-frame body, is a world first - Sony's competitors were harping that it simply was not possible and provides Sony Full-frame users with the unique ability to shoot with Image stabilization, when shooting with their 35mm primes, their 50mm primes, their 100mm primes, their 85mm primes, their 135mm primes, their 24-70 f/2.8, their 16-35 f/2.8 etc. - not a single one of them is stabilized in Sony's competition. But these are the engineering advances of the A900 Full-frame over other Full-frames in the marketplace and thus has nothing to do with your specific decision. Just something for you to mull on.
I need reasons to upgrade from my A700, my fiancee has been using my
backup
A300 for events and shes really good, but I need either another A700
or myself upgraded to a A900. I love the viewfinder, and using pocket
wizards, what else would this upgrade give me over my A700?
--
http://www.ryanhollowayphotography.com
http://www.flickr.com/rsplatpc