Sp4 is a rock. Sp3 is the perfect tire for an abrasive track. Ran one quiet a few times this year when the track was too hard/abrasive for a 2 (we just kept blistering 2's).

Sp2 and sp3 for rr depending on track conditions
D12 is a great lr, I haven't ran a d20 so no advice there

In any sense, as far as life goes I was usually getting about 2 race nights on a RR and 3-4 on a left rear. Again, just depends on the track conditions and how "competitive" you want to be. Some people throw new ones on each night, others run them until theyre pavement slicks. lol