sorry i did not see the low kv motor, with 1550kv motor i would just run the smaller spur 46-52 and gear accordingly using brians speed chart. 4s is good for tight tracks but if u get in the wide open 5s is where its at, 6s is usually heavy and not worth the gain.
this will help you figure your gearing. with 5s i would gear for about 40-45 and 4s about 30-35
http://www.scriptasylum.com/rc_speed/index.html