Have you considered a Jelco SA750D?
Far more widely compatible with a greater range of carts than any of Rega's arms IMV & much more accurate/easier to tweak/adjust, although a 'Shuggie' after market arm collar is a prerequisite if you are in the habit/want to swap carts in/out regularly due to repeatedly accurate lack of azimuth errors* (*these can be reset w a H/shell that allows azimuth adjustment, but will need adjusting each time you change a cart otherwise. Here's the link to Hugo's*(*Shuggies) thread over on AOS>>> .
http://theartofsound.net/forum/showthread.php?7359-Custom-Arm-Mounting-Collar-for-Jelco-SA-750-essential-for-setting-correct-azimuth.
I've used Rega arms fairly extensively in the past & my last arm wuz a Michell Technoarm, which is a ground up rebuild of an RB250, the Jelly 750D is far more capable with all the carts I have tried so far. In the case of my Ortofon Rondo Red it has unlocked potential I wasn't even aware of. On the Technoarm I always felt kit to be a little bland & ho-hum, undoubtedly civilised, just a little boring. It works a treat with the Jelly tho' & simply has more Joi de vivre & is now on the same page at least as my AT33EV. :stereo:
I've not actually heard the pricier RB700/RB1000, but have the RB600 & the newer RB251/301 & if buying new I'd be looking at the latest Audio Notes, or offerings from Jelco instead. Perhaps Roksans Nima would also get a squiz, although this is another which I am unsure how widely compatible they are. Rick & Stewart Banditpilot/Stewartwen have both run Nimas tho' so could advise I'm sure. :^
