According to BrewWiki:
Summit is a recently-released high-alpha (17 to 19% AAU) hop variety. It is a dwarf variety grown on a low trellis system. Because the low trellis is not machine harvestable, these hops are gently picked by hand in the field and are, assumably, less damaged by the harvesting process. Chumulone levels are low at 25-28% of alpha. Summit is said to have strong orange and tangerine citrus notes in its flavor, making it ideal for brewing American style IPAs (especially IIPAs) and Pale Ales.
Specifications
Typical Use : Bittering
Alpha Acid : 17 to 19% AAU
Origination : USA
Characteristics : Citrus (orange, tangerine, grapefruit)
Styles : American Pale Ale, American IPA
Similar Hops : Cascade, Amarillo
I just ordered a pound of Summit with the hopes of getting similar traits to Cascade and Amarillo, but in much smaller quantities.
I've heard from several folks that Summit is outstanding as a dry hop addition.
Summit is most like Cascade, of the hops you have in stock. I'd go ahead and use Summit, but in much smaller quantities. Use Beersmith to calculate.