Here's the way I see it.

The only difference between the x85 and x75 is that the x85 has more power. The only time you need that power is if you need to graph something well over 100 feet deep.

The only difference between the x75 and x65 is the type of backlight and the pixel count. Use the x65 and xoom in to 2x and you're essentially viewing at 320x320 pixels. Ok, so you can't view the entire water column as good, but if you put the x65 on a split screen zoom I doubt you'll miss much information.

So buy the x65 and use the extra money to get a water temp display.

All those extra pixels on the x75 sure are NICE though...

Nicolo