^^ I think he may have been talking to Mike..
I think they are both nice cars... Like said before, I would just go with your feeling.
It all depends on what you want in a a Mustang. The fox will feel completely different from your car. It could be good, could be bad, thats up to you.
Although, If I had to pick between those two cars, I would go with yours... hands down.
Part of modding cars is getting to your goal by yourself. Building your own car comes with a sense of security, that you know whats been done/how it's been treated etc... and buying a car already built lacks that security. Who knows whats in store for the future.
It could be a really good car, it could be bad.
If you end up trading, have a performance shop look at it, or if you can, do it before any transaction.
^^ MY .02
Good luck!