In exactly the same situation a few months ago, I referred a family member and we both got the maximum by being careful with the referral & application sequence:
1) The referrer must send the referral form (fax is most reliable) BEFORE the other party applies for a card.
2) Then, the new-card applicant is free to apply for ANY offer and will get the benefits promised in that offer. Just call and say you want the 10K deal; the 5K offer on the referral form is irrelevant because it's not the offer being applied for.
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Wright Brothers Were Wrong