Regarding Interconnect delay reduction in a design.

Then try adding one more register in the chain:

Reg1 --> Combo -->Reg2 --> Reg3 --> Combo --> ... Reg4

The fitter will optimize the path between Reg1 and Reg2 to meet timing, it will optimize the timing from Reg3 to Reg4. The path between Reg2 and Reg3 should be easy to meet timing. But if this is not the case, e.g. if the destination is too far away from the source, adding yet another extra register between Reg2 and Reg3 will give the fitter even more headroom to meet timing.