use this calculator to estimate speed and gearing...it will also show you rpm's related to your chose gearing...
http://www.scriptasylum.com/rc_speed/index.html
plug in the variable and it will help you out. As far as temps go..we all like to keep motor temps below 150. Not sure on max. voltage
1. MBX-6 T8 1900KV, RX8 ON 4S
2. MBX-5T 1520, MMM ON 5S
3. MBX-5 ONROAD CONVERSION 1515, MMM ON 5S
4. MRX-3 ON ROAD CONVERSION 1512, MMM ON 6S
5. TEN T 2650 T8, MMP ON 3S