You say you don't want to buy any upgrades, but you should at least get some L2 cache. macsales.com (Other World Computing) sells 256k L2 cache sticks for the 6100/7100/8100 machines for $.25 USD. Yes, you read that correctly - twenty five cents, or one quarter!

You'll probably pay more than that for shipping, but since you use your 6100, it's well worth it. You'll get tremendous bang for your 1/4 buck.