While I am not recommending any one over another, this is really what the networked (those little boxes) on the cables are supposed to help with. Transparent for example, where the networks (from what I understand) address this as though your 25-30 foot run is no different than a 1 meter run. Also, I would think you would consider a shielded cable for the protection against RF, etc. . .
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It depends on the output impedance of your preamp and the combined impedance of the cable and the input to your power amp. Ideally, the ratio should be 1/20. If you are unable to do the calculation, the best method is to use very low impedance interconnects. And if you do get into trouble, a buffer, such as the Musical Fidelity X-10D is specifically designed for these situations, though adding another active device into the chain may be less than desireable sonically.
Basically you want low capacitance and good shielding and noise rejection. How "low" is "low" will depend on the output impedance of your preamp at high frequencies.
If your preamp's specified nominal output impedance (which is probably a reasonable approximation of its impedance at high frequencies) is below say 250 ohms or so, a good low priced choice would be a cable that utilizes Mogami 2534. Markertek, among many other places, supplies it in rca form.
If your preamp's output impedance is significantly higher than that, you should choose a cable whose capacitance is less than around 20 pf/ft (picofarads per foot). Blue Jeans Cable would be a suitable low priced choice, although its noise immunity would not be as good as the Mogami's. Many high priced alternatives are also available.
Dan -- Just saw your post. Great minds think alike!