I was waiting for a 320 pilot to step in, but you'll have to settle for an old Jurrasic pilot's opinion.
Anytime you are off your optimum altitude, it will cost you some fuel. If you keep that 1000 fpm to 10,000', it will take 25 minutes to get from FL350 to 10,000. That'll take a heck of a lot of fuel. But I think you are asking if a "gentle" push over 10-20 miles earlier will cost any. Sure, it will cost a little, but not enough to make a difference. I doubt if it will amount to 200-300 lbs.
Configuring early will cost more, or adding 5 miles or so for spacing at pattern altitude.
But why leave optimum before you have to?
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