Improving Sequential Writes on RAID5 - Write back to SSD?

I have a RAID 5 array consisting of 3x 5TB WD Red NAS drives. RAID 5 is done via a Dell H710 HW RAID card (LSI 2208 I believe).

This is a home setup, and the pool is only really used to save recorded content (large 100GB video files) to it.

While it's not a major problem, I would like to try and improve the write performance, as currently it goes at around 200MB/s for the first few seconds and then drops to like 30MB/s (which makes sense, as it is most likely writing to the 512MB cache and then offloading to disk and hitting the slow disk writes).

From everything I have read online, enabling CacheCade will do nothing for me, as CacheCade stores frequently accessed files on the cache, to speed up random reads.

My question is, if I put an SSD on the array as a cache disk is there any way I can perform write-back to the SSD? So say I get a 128GB SSD, if I do a 100GB write to the pool, it writes the whole thing to the SSD, tells Windows the transfer is complete then in the background it writes it to the pool? I'm thinking the flow would be like Source data --> NV Cache --> SSD Cache [tells Windows transfer is complete] --> HDD Pool

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