I am totally in the dark about modern fishfinders. I'm looking at these two.

Lowrance Mark 5x DSI Gray-scale $299 + $50 mail in rebate making it $249

Humminbird 570 DI $299

Looking at them in a BPS magazine the Humminbird's actual images look clearer and more detailed but still...I know nothing about the features and don't know which will be better. I'm mostly concerned with clarity and detail of structure, bottom composition, and thermocline exposure. Navigational features are less of a concern to me. I'm trying to stay in the $300 range. I figure if I stick to gray-scale I can get a better unit in this price range.

HELP!

I have both of these locaters mounted to my boat right now. The 5x is mounted on my console and is used for locating structure and just ranging my depth while driving. It picks up a fantastic bottom lock all the time even at 35+ mph and has adjustable ping rates and screen scroll settings that make it perfect for driving and scanning for structure and/or saving your prop. The 570Di is mounted on the bow of my boat and I use it for locating fish and seeing the structure in detail. It holds a bottom lock pretty well and has no problem with interference from my trolling motor. The two are d**n near a horse a piece in my opinion, the Di is nice if your are moving slowly or are mounting it to the bow of your boat, the 5x has what seems a more definite bottom lock and I prefer the menu setup.