Bob -

As someone currently stuck using an underpowered, backup PC, I usually run a quick 'lighting check' run at low resolution (200 to 300 pixels wide) and level 3 quality; that's usually enough to sanity-check most lighting options. (IIRC, only a few, higher-level ray-tracing features [reflection, refraction] show up only at level 4.) Once I've adjusted lighting to eliminate burnout and shaded areas, I render at full size and level 4.

Maz