first of all i'll say it's not worth getting busted by the cops, i know in melb they've cracked down on L and P platers riding large bikes so i guess it would be same in syd or elsewhere.

as for comfort the best thing is to go sit on the bikes and see what is best for you, as everyone is a different size

as for actual drivability the 600's are smaller so they are alot more chuckable around corners, generally 1000's being bulkier are a lil slower around corners but rape 600's on the straight.

realistically you can't legally use the power difference between the two, the main difference will be on the track down the straight.

the current cbr600rr's are VERY nice