Hi woodchip, can't see any problems there. As you remember, I'm running a similar setup to you and same temperatures. I installed just one extra case fan to the top rear of the tower unit, next to the PSU. Sys. temp. dropped immediately from 37c to 28c and has stayed that way.
Because of the system temperature dropping, it also reduced the CPU temp. but only by 2c. from 49 to 47c. j.