Hi,
Do understand your dilemma, think you've got to ask yourself what you need first. Both cams have their share of strengths and weaknesses, and offers some comparatively different functions although they share the same platform of the leica lens, OIS n 12x zoom.
Though I am an FZ10 user, I am not going to be biased here against either one, but just to help you in listing what I know of the FZ10 and heard of the FZ 5.
Understand your concern on the noise. All 3 of them have about the same sensor n the amount of noise from pictures of all 3 is about the same, which is understandable. After looking though some sample photos on other websites taken from the FZ5 though, it seems like it applies in-house noise reduction, n some pics can look quite 'painting' like. Not very sure whether the NR can be disabled like the FZ20 though.
First, before I go into comparing the FZ10 n 5, let me compare e FZ10 n 20 for you. They are about the same breed, except of some minor improvements such as the FZ20 offers 5MP, venus II engine resulting in slightly faster focus times, diff hand grip n some slight changes to the external outlook. Retails about $910 for FZ20 n $699 for FZ10.
The FZ5, as compared to the FZ10/20, lacks the option of an external flash horseshoe, flexibility of attaching adaptors, n most imptly the manual focus. FZ10 has ISO 50-400 while FZ5/20 goes from ISO 80-400. What it gains though, is the small size n faster focus. If you do not need e extra manual focus, external flash n to attach conversion lens, the FZ5 is good enough for PnS, cos it was modeled that way.
A clearer comparison of the FZ5 n it's larger brothers can be found here.
Link:
Do not take our words in this forum for it. Have you gone down to try the FZ5 n see for yourself whether it suits you? Good luck for whatever you wish to purchase!