I would stick with the 6 inch f/8 as this size with a 6-7mm eyepiece will give the best views the atmosphere will support ( except the few perfect nights ) .
Use the 6 inch and enyoy what it will show you , and thats years of viewing the night sky .
And in the future if you want to stay sky watching and ' Aperture Fever ' hits go for a 10-12 inch Dob and keep the 6 inch for an extra smaller scope .
Use what you have and enjoy .
I to , as AstroTraveller says have the orthoscopics 5mm -25mm and they are the best in a longer f/l scope like yours , but the Hyperion are very good as well .
I would stay at 200-250x max , thats the sweet spot in most scopes , as I say that the atmosphere will allow .
Learn , take your time , enjoy and most of all
.
One more thing , do you have a RA ( right ascension , sometimes called a 'single axis drive' ) drive on the mount ? if not this would be a good investement for around the $100 mark , and easy to fit .
Brian.