started at 50x15 when i first started riding fixed. which was pretty stupid. dropped to 50x17 then 48x17 and now i run 47x17 which i'm pretty happy with. high enough they i don't get dusted be every second roadie. low enough that i can skid and tackle hills without too much grief.
i've been tempted to drop to 45x17 for some more spin.
45:18 here man, you'll love it, once used to it.