One overlooked and very useful tool on the Universal Audio web site is their UAD2 instance count chart.

The basic rule of thumb is that the more modelling that takes place when creating a plug-in, the more DSP gets used, you can see from the chart below that the new 1073 Preamp & EQ Collection takes around 10 times the DSP resources of the basic Neve 1073 and almost 30 times the resources of the 1073SE.

The chart below shows how many instances you should expect to get from the device you own.

If you do find yourself running out of juice, then go really retro and commit as you go.