Our 51% defense prevents any spike in hashpower from creating blocks too quickly as a result the difficulty is a bit slower to adjust than it should be, and thus the amount of rejects high as your competing with other pools. (Because your finding more blocks than you should be).
Try to think of it like this,
The whole network should be finding 5 blocks every 9 minutes.. but since difficulty is a bit lower than it should be, the network is actually finding 15 blocks every 9 minutes.. so 10 of those blocks end up as rejects.
The difficulty is based on the median time between blocks.. thus only stable changes in hashrate have any effect in the rate at which you find blocks.
In otherwords if you have a large pool/large amount of hashpower, it is actually in your interest to mine for 120 blocks(they don't have to be your blocks) or more at MINIMUM such that the difficulty code adjusts the difficulty to a higher value. Switching to whats most profitable(what multipools do) will only hurt you when mining GoldCoin... steady mining is rewarded and here is how:
Now imagine the following scenario:
The total network hashrate is 30MH/s and the difficulty is some low value like 0.7
You have 20MH/s and want to mine the coin,
At the beginning(ie: for the first 60 blocks since you started), your share of actual accepted blocks will be something like 5% even though you own ~66% of the network.
As the difficulty adjusts though, your portion of accepted blocks grows larger.. until it reaches the expected ~66% but these blocks may or may not be back to back.
For this reason, it is extremely unprofitable to 51% GoldCoin.. as you'd not only need a massive amount of hashpower, but you'd have to mine the coin long enough to cause several difficulty switches and even then you'd have to get lucky to get 6 blocks in a row.
Predicting when you will get these 6 blocks accepted in a row is extremely difficult.
Essentially the client will only allow blocks that have been mined with reasonable timestamps ie: no more than 6 blocks exactly every 10 minutes.
Any faster and they will be rejected. Because of this, it is possible to mine for the next block ahead of time (since you can calculate the next acceptable timestamp and only announce it to the network when it is within 45 seconds of the current network time. This feature has been built into the latest client to prevent any foul advantage doing this might have. However it is still advantageous to do this... since it gives you a 45 second head start so to speak on everyone not running the lastest daemon. For this reason I recommend pools to update to the latest daemon.
Read this:
https://www.gldtalk.org/index.php?topic=738.0Also for pools, they should update to the latest client to lower their rejects.
