Found these. Some sound like their old medigun ideas, but others I have never heard about before.
"Attrib_ClipSize_Positive" "+%s1% Clip size"
"Attrib_ClipSize_Negative" "%s1% Clip size"
"Attrib_UberchargeRate_Positive" "+%s1% Uber charge rate"
"Attrib_UberchargeRate_Negative" "%s1% Uber charge rate"
"Attrib_DamageDone_Positive" "+%s1% Damage done"
"Attrib_DamageDone_Negative" "%s1% Damage done"
"Attrib_HealRate_Positive" "+%s1% Heal rate"
"Attrib_HealRate_Negative" "%s1% Heal rate"
"Attrib_FireRate_Positive" "+%s1% Faster firing speed"
"Attrib_FireRate_Negative" "%s1% Slower firing speed"
"Attrib_OverhealAmount_Positive" "+%s1% Overheal bonus"
"Attrib_OverhealDecay_Disabled" "Overheal bonus doesn't decay"
"Attrib_OverhealDecay_Positive" "Overheal bonus decays %s1% slower"
"Attrib_OverhealDecay_Negative" "Overheal bonus decays %s1% faster"
"Attrib_HealOnHit_Positive" "+%s1 Health on hit"
"Attrib_HealOnHit_Negative" "%s1 Health on hit"
"Attrib_CritChance_Positive" "+%s1 Critical hit chance"
"Attrib_CritChance_Negative" "%s1 Critical hit chance"
"Attrib_CritChance_Disabled" "No critical hits"
"Attrib_AddUber_OnHit_Positive" "Add %s1% Uber charge on hit"
"Attrib_Medigun_CritBoost" "Ubercharge grants 100% critical chance"