Modded C6 to M5?

I currently drive an orange c6 with a 402 stroker and 4.10s that pushes 489 to the wheels. I like it but I've done so much to it, it's not even fun to drive anymore as a DD. I'm 6'4 and 225 lbs, 30 yrs old and raised on the drag strip so I'm car crazy. Had the cC6 for 3 years now.

I'm thinking another C6 or Z06, Cayman S or M5 want to spend around 40k and has to be 06 and up.

Leaning towards the M5 for comfort, power and luxury.

C6 and Z06 would be similar to what I have now and not as roomy as I would like plus I don't think I could get a Z06 I like for around 40k.

Cayman S is cool but not sure about 300 hp, a little low for me.

So is there anything I should know about which model to look for or best options? I don't want a standard luxury sedan so it'll be the 7 speed auto but read 06 and 07s had issues? Any light shed on this subject would be great. Thanks! Also best warranty and annual maintenance costs.