It's not optional. You have to claim the entire loss this year and must use the maximum $3000 allowed. The $7000 must be carried forward, unless you are able to off set some of it by realizing other capital gains.
If you question is, "should I realize gains to offset the loss this year or carry it forward to next year", you would need to do test returns to compare. This tool may be useful: http://turbotax.intuit.com/tax-tools/calculators/taxcaster/
