not sure what the exact cutoff is for each overall on the curve, but patience is the key stat for re-signing. from what i've seen if somebody has a 70+ patience you can pretty much re-sign him to kingdom come even w a 90+ overall.
haven't seen somebody refuse a LT deal during arb3. i have arb'd a guy 3 times and then refused to sign an extension citing the arb, so i suppose it's possible after 2 if the guy has a low patience.