Sheldon doesn't work for you. The basic problem is your cassette is not friendly to your knees. It has 2 knee unfriendly shifts: one at 17% and one at 14%. Here are the gory details. [guessing on teeth, as sram doesn't give exact teeth count. Of course, you can count the teeth to verify]

Gears: 42 12-13-14-16-18-21-23-26
--- ------- -------- ---------
SP CRxFW GI GIdf
--- ------- -------- ---------
1> 42x26 43.13 13.04%
2> 42x23 48.76 9.52%
3> 42x21 53.4 16.67%
4> 42x18 62.3 12.50%
5> 42x16 70.09 14.29%
6> 42x14 80.1 7.69%
7> 42x13 86.26 8.33%
8> 42x12 93.45 0.00%


So here are your best shifts, notice this sequence gets rid of the 17% shift.

Gears: 30/42/52 12-13-14-16-18-21-23-26
--- ------- -------- ---------
SP CRxFW GI GIdf
--- ------- -------- ---------
1> 30x26 30.81 13.04%
2> 30x23 34.83 9.52%
3> 30x21 38.14 13.08%
6> 42x21 53.4 7.14%
7> 30x14 57.21 8.89%
8> 42x18 62.3 12.50%
9> 42x16 70.09 14.29%
10> 42x14 80.1 8.33%
11> 52x16 86.77 14.29%
12> 52x14 99.17 7.69%
13> 52x13 106.8 8.33%
14> 52x12 115.7 0.00%