Personally, I think it would be better to remove reference to Maker vault stability fees (borrow rates). There are pretty significant differences between Maker vaults and Compound (Maker oracle delay, differing liquidation ratios, etc), and Maker has a bit less liquidity constraints so benchmarking optimal borrow rate to Maker vault rates might lead to the optimal rate at Compound being too low to preserve market liquidity in some cases.
Spitballing here but I think a reasonable DSR IRM could be something like:
- Base rate: DSR (currently 1%)
- Optimal rate: DSR + 3% (currently 4%)
- Max rate: DSR + 40% (currently 41%)