First off creditboards.com is solid advice.
You have cap 1, best buy (assuming hsbc, some are chase) and sears (citi)..only the last is SOMEWHAT flexible in my experience.
The student excuse doesn't help always, in their eyes your judgement meat..don't pay, we get a judgement and have 40+ years to collect. Of course there's a cost in that, and that cost is 20-50%.
First offer on all should be 50%, let them come back and if they say no, don't budge..badger them at 50% until they move.
Now, re: your score..are you sure you have near 600 scores..with current 60/90 lates that's high. It won't move until these have been cleared 90-180 days, then it will bump. After a year with good history it will move again then 2 years should be minimal effect if all else is good. Keep in mind you need positives reporting too, if you have no other credit, it's unlikely to help your score as much (thin file, nothing to support your score credit wise positively) you don't get a good score for no debt, you get it for responsibly managing debt. There are guys with hundreds of thousand in debt and top scores, and people with no debt and low scores.