On 738 fleet we adopted the policy if the flight is more than 1 hour we can climb above 360, less than one hour below FL 360 as the TC and TD result in a very short cruise sector. But to answer the OP, on a 55 min flight we could normally easily achieve 350. in terms of performance, at average take off weights 65-68 T climb rate was between 3500 fpm below FL 320 and 1500 fpm above 320, then 1000 fpm from 320 to TC. In other words 15 mins after take off we were in the cruise at FL 350 if ATC allowed.