What used speakers would you buy under $600?

I have a B&K St-202 amp and Pro 10MC pre-amp. What speakers will provide the best sound for less than $600?? New or used?
agree on the Spica suggestions ... older but very viable even in todays crowded market.
1. Linn Katan
2. Spendor S3/5
3. Quad 12L
4. GR Research Paradox 1

All used at around $600, maybe more $ for the Katan. I've owned em all and prefer the Katans over any including the Totem 1 sigs and Arro.