I'm guessing at some things since the information wasn't provided, but here's some observations:
You have 128 LRU's (good) but 128 CLEANERS (bad, since you only have 4 CPUVPS threads defined. I'm assuing 4 physical CPU's, so those cleaners are all fighting.
It looks like the majority of the "writes" occure on dbspace rtlogidxa. Cleaning that will be your bottleneck.
You are not running Fuzzy checkpoints - why not?
You have allowed AIO to take the default of 2*#chunks, yet you don't use AIO, so you have idle AIO threads just messing things up.
Physically, where does your physical and logical logs sit relative to rtlogidxa and rtlogdatac.