Poor performance incremental publishing

We are using CM 7.2 with a SQL 2008 database running on a separate database server. This is running in a virtual environment and we have recently upped our DEV SQL server resources to match that of production (16GB RAM).

Our DEV performance is considerably slower than production when it comes to publishing large sites (incremental) with 50,000+ content items. Smaller site pub times are reasonably good.

The SQL server CPU usage is running at around 99% while the content list is being created and a publishing run which takes around 15 mins on production is taking between 6 and 30 hours on DEV.

This generally only happens with incremental publishing and if I clear down the publishing logs before running an incremental, the publishing run takes around 2 hours, which is similar to production.

Can anyone think of a reason why, when there is data in the publishing logs, incremental publishing would be so slow? SQL configuration? Network?

Thanks

Chris