We kinda use our own.
Clerics can use any creature that shares an alignment with the cerlic's god. So a cleric of a chaotic good god can summon CN, CG and NG creatures, aw well as anarchic and celestial templated ones. In addition, if a god offers an elemental domain, they can summon cratures with that elemental template - eg. if a god offers the earth domain, the cleric can swap other templates for earth. The template thing only works for animals basically, as seen on the core list. But I allow any animal on there, so a cleric could summon a celestial, anarchic or earth snake for example.
Wizards can more or less summon anything they like. They need to speak the language to summon elemental templated creatures or alignment templated creatures (fire needs ignan, celstial needs celestial etc) and they need to make a spell craft roll to add them to the list. But the list is of unlimited size. I think this is too strong, and next campaign i'll probably use modified UA rules.
As far as slowing the game down goes, it doesn't. If a player has their head around the rules and the creatures they can summon, all well and good.But there's no spending 10 minutes in a combat trying to deide what to summon.