Thanks for all the help its given us a place to start looking deeper at the issues.

To clarify a few points,

1) The SQL Install on the DB server is dedicated to Sharepoint DB's and its the only thing running, that said knowing the infrastructure people who do the install they've probably done a tick-box next install.

2) The PLE timing should have been in seconds not ms so should have read 150-200 seconds (my bad!!!), still lower than I would expect but more acceptable, than 20000 seconds.

3) Disk through put Read/Write times are consistently 7-10ms with peaks of 0.5 seconds under heavy load.

4) Data throughput were pretty much balanced between reads and writes having 250-300kb/s each, Id like to get this higher but I think we've been allocated a slice on a disk rather than dedicated disks on the san.

I agree the memory is the key especially the max level, but I've generally worked on an initial 75/25 split for the DB/OS, but that was mainly on server 2003/2008, these are using Server 2012 as the OS, so I'm not so familiar with the set up.

I was thinking of starting at a 60/40 split, so approx. 20gb for the DB and 12 for the OS, and then running a monitor to check how things were going, and adjust accordingly.

I checked yesterday with the admin and its now idling along at 7 docs per second, but there are 4 docs that are causing errors, which the SP admin thinks could be memory pressure as they are a few 3-4MB in size, or a corruption.