Just so you're aware, the higher watts you go for vaper production, the less flavor you're going to get. It's the trade off.
The M Pro is regarded as one of the better subohm tanks on the market atm for DL vapers. The 904L coils are quite hardy and last a long time if used correctly. There have been reports of the coil dry hitting within the first day or so of use, which people automatically correlate with the coil going bad. I would check to make sure you're tipping the tank to the side or even rolling it around to allow the air bubbles forming in the coil to release out of the juice ports. Are you seeing little bubbles flowing out from the coil into your tank after you vape it? The heat is something that simply can't be prevented. Is the tank getting too hot to touch your lips to it? Are you feeling your mod heat up? What is too hot about the tank? The vape you see coming out of the chimney after you vape is the coil cooling down. Kanthal generally has a longer heating period as well as a longer cooling period. There's nothing mechanically adverse about the vape fizzling out after you fire it.
If you're looking to try and cool the tank down some, there are these that may help:
$1.74 Replacement Heat Insulation Gasket for Atomizers (5-Pack) 5-pack at FastTech - Free Shipping
$2.14 510 Heat Dissipation Heat Sink for Atomizers - stainless steel / 25mm diameter at FastTech - Free Shipping
The latter being the better option for cooling.
Your coil isn't likely "blown". You may taste some burnt flavoring for a few vapes, but that should go away. I would recommend sticking to 60w if it's working for you. The M4 coil itself ranges up to 110w, but that depends on what the coil is reading for ohms. Also, do you carry your vape around in your pocket, or knock it around at all?