I am looking for a lilac with a fragrant, lavender bloom. I am in the Seattle area in Zone 8. The planting location is in direct sun from the East and West approximately 6 hours each day. I am look for a variety that is rather compact. It should not grow higher than 6 to 8 feet at maturity.
Forgot to mention Lilacs 'Miss Kim' and Syringa microphylla 'Superba', which sometimes repeat blooms in the fall, but is more of a pink. These three are compact and should be within your height requirements.
For large flowerheads with strong fragrance look for S. vulgaris varieties. These are staples at local outlets, what most people know as lilacs. Independent garden centers here display multiple named cultivars during the peak season. At this time of the year selection liable to be reduced - but so are prices. And fall is the best time to plant winter hardy stock.