which is better in speeds, load carring, dependability

45 mag since it's a true 45hp engine. Add iron mountain heads and dual carbs and you have yourself a 7000. I have a 5500 and I'm happy with it but 5500 has all factory internals while the 45 is completely modded.

since it is completely modded would it still be reliable

The motor is reliable, its the abuse and how you treat it that determines the life of the motor, motor can make a 1000hours if you treat it right.

Do a search on here but I don't there too many 45 mags have blown up. Like take'em said, it's all in the way you treat them and maintain them. Really the only advantage to the 5500 is that's it's the newer CDI type engine. Mine does great on the top end but it's a bit lacking in the bottom.