In general, drivers aren't interchangeable.

Without sensitivity matching (and a few other things) you may end up with crap frequency response... And it can be tough to figure out what's going on. It can even sound good if its just louder in the right places by making you hear things in a new way, yet still have bad frequency response. Lots of big box speakers play these tricks to stand out in a crowd, but the reality is they grow very tiring to listen to at best... And get the wrong mix of parts or wire up wrong for those parts and you can end up with big holes in the sound...

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Does any one knows if this C5 650 will fit in this car?? As per this post I am not sure at all.

Also does any know the amp measures?

What Bluetooth issues do you have? I've been considering this head unit because I like Android Auto and the physical volume knob but I pretty much only use Bluetooth so that's got to be reliable.

When I turn on the engine and the head unit goes on sometimes - is not all the time - I can't connect the phone over Bluetooh, I am not sure if it's a problem from the Unit itself or from the wiring

I just did a front-mid install of jl audio c1-400x, you can check it here.
I also thought that it woul'd not make much of a difference but to my surprise it did. So I woul'd rather suggest that you give it a try. You can check speakers in these locations just fixing the wires with electric tape to the harness (once OEM speaker removed) and see for yourselves befor fitting anything. I agree on the rear speakers though. They do not do much. I also like to fade the sound a little bit forward and to the passenger side. That's how I feel my system is more balanced. But that's just me. :popcorn:
PS: @Chimera I woul'd thank you for the threads and comments also but I do not have the option to do so, yet.