there's plenty of people using 700's behind power.if you have any reservations about it you should talk to the guy building the trans for you as he'll be able to answer any concerns you might have about your future trans and go from there.
I would be interested to see the applications, power level and how long they lasted. Make me a believer....I really don't want to spend the $$ on a new trans but billet parts for 700R4's just aren't available like the 200-4R.
Finding someone that will warranty a 700R4 for anything over 600 hp power level could prove challengin.......I've been looking. I really like the way my truck shifts and it was built with all the best parts (commercial clutch pack, big boost valves, modified line pressure, hardened input shaft, modified stator support, etc. etc.) but my builder says it's only good for 400 hp. You might be OK but if I where you I would go with either a 200R4 or a pre 2004 4L80....Yes, you do need a transmission controller. Many say a stock, untouched 4L80 is good for 650 hp.
http://etereman.com/blog/general-mo...before-you-buy-a-gm-with-a-700r4-transmission
https://www.camaros.net/forums/27-t.../61127-why-cant-700r4-built-take-high-hp.html