You stated a couple of things that make this easy: 600.4 amp for sure and want to stay with coax. Get the moto 602s, run the 600.4 bridged and be done with it. The amp and speakers were made for each other. I ran the 602s for a season and they're still my favorite coax when you give them the power they like. Nothing wrong with the millie 165.3 or upper end focals, but I really liked the sound of the the 602s with 200-220W going to them and listen to primarily rock.
That being said, the power piece is important - they sound pretty good at 150W, better at 180W and they really perform at 200W. If you're going to use the rear channel of the 600.4 to run the 6900s later on, then you may want to go with the higher sensitivity 165.3. After running them at 180W-200W, going back to 150W would be a noticeable downgrade to the front stage. The front stage is the most important piece of the puzzle. In a 4 speaker setup lids are just lipstick on a pig if the front end isn't solid.
The good news is you can't go wrong. Any of the 3 will be a night and day difference to JM, yes I've ran them before too. The 602s,165.3, and upper end focals all have their strengths but it's really splitting hairs when you listen to them side by side and a lot of it simply boils down to sound is very subjective. I may like one better than the others and you may prefer a different one, but none of them are bad and to get significantly better performance you'd have to go components and really match the amp to the speakers.
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2018 CVO RG lava orange, 117 Stage 3, 14" F47 and a few chrome extras. Boom crap gone.
2016 RG Special Cosmic Blue, 120ST with Dragos 2:1 and TTS tuner, FBI drop seat kit and JNR air ride. Stock audio long gone.
Last edited by roadie13; 10-15-2017 at 07:15 AM.