What can these motors handle?

After about 450 rwhp the fuel pump needs to be upgraded, usually a GT500 pump is used. Supercharger kits come with fuel injectors usually. The clutch usually depends on how hard you are on it. If you just drive on the street they hold up pretty well, but if you have sticky tires and beat the snot out of it the stock one gives out. I have an M90 based Roush supercharger and I still have the stock clutch.

After reading many posts and talking to guys at the track a safe bet is to stay right under 500rwhp. If you are going over that you might as well take the plunge and beef up the internals and not worry about anything. Up until earlier this week I spent a lot of time reading about FI because it was my next step. Now I just need to figure out if I will have my Mustang or not in the next few months.

I wouldn't trust rwhp numbers. They vary so much from operator to operator and dyno machine (mustang to dynojet etc). There are two dynoshops in my area. The mustangdyno we use now offered 20% lower numbers than the dynojet we used to use (at the same boost and power level).

Some folk use our guy with the mustangdyno to get their race tune and then go up the street to get a couple of pulls on dynojet to get the dynosheet with the higher rwhp number.

I doubt that our tuner would go over 430-450 rwhp on a stock motor.

My daily driver supercharged 07 GT automatic made 364 rwhp on a MustangDyno (which would likely be about 400-410 rwhp on a DynoJet) and it is very conservatively tuned for daily driving duties. Blower has been on the car 1.5 years with no problems for my drivetrain and that's with a fair number of racedays at our local dragstrips.

The blower I have is non-intercooled, but even it came with 39# injectors and a 2nd fuel pump as most blower kits come with fuel upgrades.

I personally think the weakest link is the connecting rods (they're about as big as a toothbrush!). Also, get a bad tune that's too lean and you're asking for trouble quick. The transmissions (manual and auto) are very stout, and the 31-splined axles in the S197's are very tough.