Back in SR3, you could default to a similar skill or an attribute when you lacked the skill you need. Now you can only default to an attribute with a -1 die penalty.

Assuming there was a list of "similar skills" (or even just by using the skill groups as a reference), would defaulting to a skill be a viable option or would it be "overpowered"?

How about a -2 penalty if you need to use a skill that you don't possess, but you do possess another one that fits in that skill group?

Ex. I have Agility 4 and Pistols 3, but the only thing close by is an AK-97 and a dozen go-gangers. Under normal rules, I'd have 3 dice (Agi 4 - 1 penalty), but if I was able to default to Pistols I'd have 5 dice (Agi 4 + Pistols 3 - 2 penalty). Even if I had only 1 Pistol skill, it'd still come out to the same as defaulting to the attribute (Agi 4 + Pistols 1 - 2 penalty = 3).

Would this undermine skill groups? I don't think so, what's your thoughts?

My immediate thought is that it would make skill groups irrelevant, and given that they are a concept I like, I'd not be keen to let skill based defaulting in to a game I ran

Defaulting to attributes is just fine., for game balancing purpouses. If we are going to be realistics a bit, everyone runs around with agility 4+ since its practically impossible to not hit something 50m away with a rifle of you aim properly.. and aiming properly doesnt require a genious..

I can only say I concur.. =)