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Stefan
There are a few aspects to your question. Firstly I will limit my answer to the 130mm scope as I have some experience with scopes of this size. There is an oft quoted and oft misunderstood idea of "maximum practical power" of 50x per inch of aperture which in a 5" scope gives a theoretical maximum poer of 250x which would equate to 650/250 = 2.6 so in theory a 2.5mm EP can be used. This is purely theoretical and will require perfect conditions. In my experience the maximum is probably closer to 10x or 15x per inch or 50x to 75x in this scope. This power will give reasonable views in your scope regardless of seeing as long as the sky is clear. If it is still, then pump it up. My old 5" was a FL of 900, and I found a 10mm EP giving 90x was next to useless.
So that gives us some clues. Using your 25mm gives 650/25 = 26x so that EPO is fine. The 9mm you have gives 650/9 = 72x so that will be OK for good night. To get a mid range say a 12mm EP gives 650/12 = 54x.
So I would look for some in the 12 to 15mm range.
If budget is not a serious object the trusty 13mm T6 Nagler is a cracker of an EP, but at $339 is a serious investment. For an economical option the 15mm GSO/ Bintel superview ($49 at Bintel) gives 68deg AFOV and 15mm of eye relief.
Malcolm
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