jumping in after the decision was already made but i'm going to voice mine anyway.
option 1 - pointless. it's the same car and if you want any kind of power out of the car you'll be ditching the cobra stuff anyway.
option 2 - meh. going backwards in terms of looks and comfort. neat cars but not that fun to drive a lot
option 3 - worth it. they are SN's so the price keeps coming down and its a good platform to start from. but you'll have a learning curve with working on it not to mention it will be more costly than a 5.0
option 4 - worth it. can be harder to find for the right price but it has IRS which is nice. have to decide if you want a new edge body or not. i wouldn't though. SN95 FTW!
all that said, i'm glad you're keeping your current one.