Those 210 points from 1 s.lvl 6 SR? You spent 15 R's when you could've spent 13 R's (1 s.lvl 4 SR + 7 R's). Alternatively, if you have way too many SRs lying around, you could use 2 s.lvl 3 SRs (requiring 6 R's).
The reason you stop at s.lvl 4 for SR is that to hit 5 (and thus gain 35 more points out of it), you need to put in 40 points. So it's a net loss of 5 points/half a R. Lv 5 to 6 is eating 50 points to get out 35, for a net loss of 15 points/one and a half R's.