Cash-on-Cash 4.5 later 6.9%

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Dear All,

We are working and living in Switzerland and invested in Houston into our first cashflow real estate single familiy house which gives us a real Cash-on-Cash of 4.5% and if we would change finance from 6.75% interest rate to 5% interest rate it would result us a 6.9% Cash-on-Cash. We are new and want to learn, do you think this rate is ok or not so? the property is located at

http://www.zillow.com/homedetails/15511-Pebble-Lake-Dr-Houston-TX-77095/28372870_zpid/