Yeah the cap hits with Dak is a tough subject, especially since he already has over $100m in cap hits on the existing contract to worry about. For that reason I almost think the number of years is more important that the yearly amount. If I'm Dallas I would really push for a 6 maybe 5 year deal to spread that around more. I think your right that Dak probably wants a 3 or 4 year deal so he can reup one last time, but that just makes the numbers extremely difficult.
Just playing around with the tool on Spotrac.com a 4 year extension would look something like:
2024 - $60M
2025 - $65M
2026 - $61M
2027 - $60M
2028 - $44M
2029 - Void - $50M
Now that is without really moving the numbers around, so that 2028 and 2025 numbers are probably flipped, but we can see just how tough this contract is. Upping it to $65 is extremely tough adding another $20M, and this is why a $55m/year would be a pretty reasonably deal for the Cowboys.