5 x 6 is definitely within the realm of what he's worth.
And I think it's in HIS best interest to take the 5 year deal.
I think he could easily play until he's 38, albeit maybe not nearly as effective as he is now.
Scenario 1 - He takes a 7 year deal on the market, somewhere, for 6 mill per. He'll be 36 for his next contract, going on 37. By that point, his flaws and deteriorations will likely be very evident, and he'll be looking 1-2 year deals worth significantly less than he's making now (let alone after his extension). So let's say he signs 7 x 6 and then 2 x 1.5 and then calls it a career. 45 mill for 9 years.
Scenario 2 - He takes a 5 year deal with the Rangers, or somewhere, for 6 mill per. He'll be 34 for his next contract, going on 35. It will be much easier for him to maintain a certain demand for his next contract if his sample size is limited to 5 years. Let's say he remains healthy for all 5 years and he produces 55, 55, 50, 50, and 45 points for the years of his extension - also not beyond belief. A cup contender, maybe even still the Rangers, could look at that, look at his leadership and his intangibles, and offer him a 4 year deal for let's say 4 mill per. So 5 X 6 + 4 x 4 would make it 46 mill for 9 years.
He actually makes out better in scenario 2.
Now let's say at the end of year 5 the salary cap has gone up - i.e lets prorate the contract a little. The concept still applies. Let's say he makes 2.5 instead of 1.5 and 5 instead of 4. He still ends up with more money in scenario 2.