IIRC the 2.5 inch would be more common.

Retention on my El Paso holsters is very good. If I fully insert a revolver into the holster and then turn everything upside down, the revolver will slowly drop free after a couple seconds of hesitation. More than enough retention for me to reholster the guns and amble over to the next shooting position. If I need more retention I just use the hammer loop.

If I wanted to loosen the grip of the holster on the revolver I would put the revolver in a plastic bag and then holster it and let it sit for a day. The added thickness of the bag will slightly stretch the leather and loosen up the retention.