update on this: i FINALLY got it last night! thank you everyone for your help.
i found waves 7 and 8 the trickiest, and i ended up trying several things. i knew once i started regularly getting to a wave that i was close to figuring it out, and then it was all about maxing out my damage. the final wave (with two amber weavers a healer, and 3 smaller mobs) was the hardest for me by FAR. dealing with having to almost constantly be on the move was really hampering my damage, but scorching on the run helped me at least proc so i could chuck Pyroblasts! at things.
what ended up working for me was sheeping one of the amber weavers, positioning myself so the healer would get hit by the other weaver's blobs, then nuking down the healer. once the healer was gone, i focused on taking out one of the weavers. once that was gone, i popped Alter Time, fired up mirror images, and worked on the other weaver and the two larger shielded mobs. when the last of those went down, i realized i just had seconds to go, and my mirror images really helped here with just that extra DPS. with 5 seconds to go i ran up to the last mob and (in a bit of a panic) hit him with dragon's breath, and ta-daaa! (with three seconds to spare, haha).
my GM gave me a grey item, Medal of Patience, haha (
http://www.wowhead.com/item=114004/medal-of-patience" target="_blank).
thanks again for all the help. i'm currently vowing to never set foot in the proving grounds again, but we'll see...
