Tom,
Sounds like you're already on the right track to me! For street cars my driving experience and preference is that a 35R is as large as could really be considered responsive enough under all conditions to be "streetable" without altering your driving style significantly to accommodate a LARGE turbo. A 35R will produce enough top end that running at its full potential you can rarely find enough room on the street to let it all the way out for more than a second or two before cars, corners or other street obstacles impede your fun You may as well get the 1250cc since they are negligibly more, can still be tuned for great drivability and will prevent you from needing to upgrade an upgrade later on

Tom