Here are some examples of just how much of a game changer path guiding and many light sampling will be - especially when used together (I downloaded the many light sampling branch to conduct these experiments as it includes the path guiding additions).
Vanilla Cycles - no clamping, no filter glossy, full GI preset
With Many Light Sampling enabled (sampling all lights)
The roof is a bit odd - but it has funky material that might not play well with many light sampling. I need to figure it out - but the overall noise level is much lower, with fewer bright fireflies.
Each image is 100 samples.