Tint works is definitely where to go for a quality job.
And in terms of 60% I definitely think it's WAY too light. It would be difficult to even tell it's tinted at that level.
The legal limit of 35% also just slightly too light for me so I usually ask for 30-35% film to be applied which drops the total somewhere in the mid-20s. Illegal but I take my chances.
EDIT:
Just to clarify, are you talking about:
-60% total light passing through (approx 85% film application)
-60% darker than stock (40% film)
-or 60% film application which would drop it to approx 42% visible light transmission?
Stock glass, btw, is usually around 70%