It means that NiCad used to be able to provide more peak current, which meant highger ROF. I use past tense as NiMH has improved since then. A 600mAh mini will die rather quickly with a 150% spring, due to higher internal resistance... you'll probably get under 300 rounds per charge, depending on the weather and if your mechbox is upgraded well or not. The 3000mAh isn't a bad choice, but make sure you've got a charger that can charge NiMH batteries. Also keep in mind that in the colder months, NiCad fares better than NiMH.
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