Answer: There are many plants you could use. I would suggest since it is a slope that you use plants that prefer good drainage or well drained soil or are drought tolerant. Partly sunny can be considered full sun if there is a minimum of six hours of direct sun including the hour of noon, or if it is baking hot and sunny most of the afternoon. (If you have just a few hours of morning sun you may want to look at shade tolerant plants such as hostas and ferns, especially if you are able to water the area in dry spells.)
You could look at perennials that tolerate lean dry soil and prefer sun but do well in part sun such as purple cone flower (echinacea), rudbeckia, iris, dianthus, daylilies and perhaps herbs such as thyme. The lavender and perovskia really need full sun all day to grow well and there may be a hardiness issue with the lavenders.
Your zip code places you in zone 6A or the colder part of zone 6. If the location is windy or otherwise exposed and cold it may actually be like gardening in zone 5. So you may want to concentrate on hardier perennials rated reliable into zone 5.
Roses might be a good choice, if it is sunny enough, you could look at some of the lower growing landscape roses such as Bonica, but make sure they are grown on their own roots rather than grafted to assure better winter hardiness.
You might also consider some evergreens such as mugo pine or low growing junipers to provide winter interest.
Your local county extension and professional nursery staff may have additional suggestions based on a more detailed understanding of the planting site nad your design goals. Have fun with your project!
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