Hi,
To answer your questions, yes I load my match 223 on a 650 using competition dies with good results. (Before I got the 650 I loaded 223 on a 550.) Have to say though that for my 300-500 meter match loads I throw the powder (Varget, Vitha) with a Harrells dispenser.
The caliber change on a 550 is easier, cheaper and faster than on a 650.
Loading on a 550 is a lot faster than on a single stage but the 650 is faster than on a 550, mostly due to the casefeeder.
keeping in mind the number of rounds you are planning to reload weekly I'd start with a 550.
Cheers from Holland,
BolloX