Upgraded find familiar

at a 3rd level spell slot you maybe summon anything up to a 1 crr rating, the rest just works like how it normally would, when using a 4th level spell slot you can summon up to a 2 crr rating 
when using a 5th level spell slot you can summon up to a 3 crr rating
when using a 6th level spell slot you can summon up to a 4 crr rating
when using a 7th level spell slot you can summon up to a 5 crr rating
when using a 8th level spell slot you can summon up to a 6 crr rating
when using a 9th level spell slot you can summon up to a 7 crr rating
when 2 people join together each using 1 9th level spell slot you can summon up to a 7 crr rating
when 2 people join together each using 2 9th level spell slot you can summon up to a 8 crr rating Or when 3 people join together each using 1 9th level spell slot you can summon up to a 8 crr rating

when 3 people join together each using 2 9th level spell slot you can summon up to a 9 crr rating or when 4 people join together each using 1 9th level spell slot you can summon up to a 9 crr rating

when 4 people join together each using 2 9th level spell slot you can summon up to a 10 crr rating or when 5 people join together each using 1 9th level spell slot you can summon up to a 10 crr rating

when 5 people join together each using 2 9th level spell slot you can summon up to a 11 crr rating

you get the how it goes but there is a down side if you summon anything higher then 20 the caster minds break killing them all