vhawk,

I looked for a long time and tried out several units (from low end portables to super high end chartplotters) in friends boats and came up with the following rules of thumb before I bought mine:

1) I felt about the most important things was to get as much vertical resolution as you can on the screen. The more dots you have in the vertical, the more detail you can see, especially if you fish deeper waters (> 100') in the south Sound. For example, a fishfinder with 240 vertical pixels in 200' of water means each pixel represents 10" of water. Using a finder in the same depth with 480 vertical pixels means each pixel represents 5" of water. When looking for fish, obviously the more pixels in the vertical means the more detail you can see. Two fish close together will look like two fish in the high-res screen but will look like one big fish in the lower-res screen.

2) Color is nice... but you pay a BIG premium for it. I found that it was easier to glance at a color fishfinder than a grayscale, but in the end you get just as much information on the grayscale (all else being equal) at a much reduced price. The bottom line for me was did I want to pay as much as $200+ more for the color when I could look a few seconds longer to get the same information from the grayscale.

3) As long as you can get your transducer in clear water, location doesn't seem to matter too much. Non-through hull transducers (that mount inside the hull using special epoxy) work but the concensus was they are fussier to locate correctly and once they are installed, moving them is a major pain. Also, in theory you loose a little depth / clarity shooting through the hull. For wood or metal hulls, you must use a through-hull or transom mount. I saw no noticable difference in performance between a transom and through hull except in a few cases where a well placed through-hull transducer out-performed the transom mount at high speeds (presumably because of turbulence).

4) Transducers come in many flavors. Dual-band (20kHz/200kHz) transducers will go deeper than single band 200kHz but at the cost of reduced resolution and generally a narrower "view cone". I found that single band 200kHz transducers worked just as well as dual band everywhere we tried them here in the south Sound (water to 500+ feet deep). So IMHO, single band 200kHz transducers are just fine for the fishing around here.

4) To revisit the transducer cone of view a sec, not all transducers are the same with some providing narrower (30-40 degree) view cones and others providing wider (50-60 degree) view cones. Obviously, the wider the view cone the more you see under your boat, and that is generally a good thing.

5) Power is also a factor, with more power allowing you to get deeper and also less directly impacting the resolution detail (more power can mean a cleaner return signal). One rule of thumb I was told by a rep was for saltwater reduce the maximum depth advertised by the manufacturer by 50-60% to get something realistic. However, most 1500W units are rated to 800-900' and even using the 50-60% for saltwater rule of thumb that still gets me 400-500' of good return in saltwater (being conservative). The next step up in power is the 4000W range often rated from 1500-1800' or so, with the associated price premium. I only tested one 4000W unit (which was also a dual frequency transducer) and saw no benefit vs. the same unit in 1500W (screen resolution and everything else was the same). Also, the power ratings I list above are peak power, a number generally considered to be pretty misleading. RMS power is a much more meaningful measure of power but not all manufacturers list it.

6) Screen quality varies and this is an important consideration since if you can't see it in broad daylight it may not do you any good regardless of other features you found important. While it is possible to go into a ton of theory, I found the best thing to do is to go to different stores selling the units you are interested in and look at them in person. If you can, adjust the view settings as well since unit A may look a lot sharper than unit B until you tweak unit B to look its best.

In my experience, the Garmin units just didn't have the resolution I wanted and I ended up buying an Eagle FishMark 480 as it had the second highest vertical resolution and the best transducer of all the units I tried and looked at. The Humminbird 565 was almost my first choice (and a very sweet unit) but in the end I liked what I saw from the Eagle/Lowrance (Eagle is made by Lowrance) transducers even though the 565 had 640 vertical pixels of resolution... just one of those cases where results in the field didn't quite sync with what the specs would indicate. I suspect it is a transducer quality / RMS power issue between the units. Overall both were very nice units and both were under $200! Like you, I set the top price at around $400 so I would have gone higher and while I would have liked color, I had a hard time justifying the price premium being as steep as it was just for the color and often the vertical resolution dropped in the color units as well.

One other thought, if you are considering a combo fishfinder / GPS then I would definitely go with color and as much screen resolution as you can afford. Maps in B&W just plain suck and you need a LOT more resolution to use a combo unit effectively than you do for just a fishfinder (in my opinion).

Hope this helps...