The 3570Gs SFP ports support gig. To support 10G, you'll need the 3570's "big brother", the 3750-E series (or another 10 Gig capable switch). (BTW, there was one 3750 series switch that provided a 10 gig port, but it has been discontinued.)
As to load balancing on the 3750G gig ports, it supports Etherchannel or it can route across multiple links.
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BTW, you can stack the 3750-E and 3750 in the same stack. This allows you a 10G port into the 3750 stack.