How much power through SN95 Mustang 8.8" rear (28 spline)?

Where did you get the $1K to modify one? Services

Also I've never had an issue with 8.8's. Lots of guys drag race with them really hard in their fox body mustangs without a problem. The 28 spline axles are the weakest axle they offered, but you can upgrade the axle and carrier later if you need to.