I've read there's a nasty harmonic at 7500 rpm that will eventually destroy the crank if you don't properly prepare it, so for a stock bottom end it's probably something a little south of that.

So what would be a good combo for a nice dayly driver engine?

I have a mild cam and stock SU wiht 3*2 headers..

So what would be a good combo for a nice dayly driver engine?

Wow, I don't think there is any one answer to that question. Many people use the stock L24 with SUs as a DD and find it fun to drive and reasonably fuel efficient. As you go to bigger carbs and/or bigger cams, fuel economy is going to suffer, which I think would be a problem for a DD. Plus the power curve tends to shift towards higher rpm which isn't all that fun in stop/go traffic.

Converting to FI, especially megasquirt which you can tune yourself, could make a significant improvement in mileage, but isn't cheap to do, and takes skills that not everyone has.

For me, an L28 + mild cam with megasquirt, header/exhaust and a good 5 speed/diff combination would be a reasonable compromise for a DD that's fuel efficient and also a lot of fun to drive. Or use the stock SUs if you prefer and trade off some fuel economy.

Just as a counter point to the above, I drove my Z with triple 44's, L28 with ~8.5:1 compression, cam, light flywheel, ACT clutch, header and 2.5 exhaust in stop and go and never had any trouble at all. That should be a horrible combo for traffic, but it really easy to drive. I got low mid 20's on the highway.

My friend had a 510 with an L16 and 44's, cam, flywheel, clutch, etc, and it was damn near impossible to drive. The extra torque and mass of the long crank make the L6 much easier to deal with.