I purchased two dwarf lilac shrubs from QVC last year (I forgot the nursery they came from, but it's not a bad way to buy since they're guaranteed, and shipped according to your planting time). They haven't grown as fast as I'd like, but they seem to be holding their own even through the drought we had. They should get to about 5-6', I think. Might have to put them on steroids, though.
Thanks for your question - I'd love to have the fragrance of lilacs in my yard, and may try to grow one just for the heck of it. We had 30-year old lilacs on the end of our house in NH, they were at rooftop level, and beautiful (see thumbnail). Had to leave them with the house, though.