>Synced 1544588/3479026 (44%, 1934438 left, 0% of total synced, estimated 2.5 days left)
So far adding 20GB of bcache to my HDD has led to an incredible improvement in sync time over just using the HDD as is. Hit rate for reads is very high and the writeback cache seems to help a lot speeding things up also. Still can't give a final verdict but it looks promising.