Richidon Koi use a BBF7 with a sequence 18000s and it is fine, apparantly they get around 3500 gallons a hour. They stated that I should get around 3000 gallons with that pump acording to my pipe runs and head that I need to pump.
I then spoke with Absolute Koi who have fitted a BBF7 with the above pump and said that they have no trouble as well. They also recommended that I could put a 2" tank connector onto the side of my Ultra Sieve and attach another pump of around 1800 to 2000 gallons because the Ultra sieve can take a max flow of 5000 gallons, and not the 4500 gallons as stated.
They have done this on various pond builds and its been fine.
If I then pump the skimmer and the new pump on the Ultra sieve into the bakki shower this will give me just over 3000 gallons due to head that is required.
I could even put a Tee piece into my return from my BBF filter to the bakki shower as well and use some of the BBF water on the shower if required.
Also during winter I dont have to have all the water going over the bakki and can return the BBF to the bond mid water.
This will aslo give me more flow and current within the pond, with the bakki returning from above and the BBF in mid water of the pond.
I dont have to do to many mods due to the fact that I have 2" pressure pipe allready fitted and thats what is required, except to reduce the the pump connections with bushes and also on the Bakki shower from 2" to 3" on the spary bar.
Mike has sugested using to spary bars, and a small modification to be made on the return shute.
Hopefully I will get around 6000 gallons an hour turn over on my 5000 gallon pond.
Looking foward to doing the modification, but not looking foward to letting her indoors know how much its costing

Another plus is that I should be able to lower my pump watts from 800 to around 500 watts in total, so a little saving there

thanks for the replies
Roy