bumping before a day is counter-productive as people see that you have 1 reply and less people will bother looking at your thread.
Give me a second and i'll come up with a build.
also, unless you have some i don't believe there is any data on how many runescape windows a particular gpu/cpu combo can run. I'll give you the best for your money and be quite confident in the results, but i can't guarantee anything cause i haven't tried it.
also, are you sure you need 32GB? According to my research runescape can't use more than 750mb a piece.
Try it. Open one runescape window and check ram usage. Then open a second and tell me how much is used. The difference is the amount per game.
It's a bit above budget and provides much worse gaming performance but would likely let you box more runescape games. You would use the six hyper threaded cores by putting one rs game on each thread (or two or three or four on each). I can drop a few things down in price if you need me to.
I honestly think either build would let you box far more than 8 games, so i recommend the first one.