Had an engine built.. 500 to 540 hp in a 96 outlaw SST.

Bravo x drive. Sport tubes and open headers. does anyone know what speed I should be getting with this engine.. running Full MSD ignition. stock 96 454 thunderbolt fuel pump.

with a 26 4 blade was running 4500 to 4600 rpm.. max opperating range is 5200 rpms. was up around 70 mph.....

would a 25 3 blade mirage plus give me more speed and stability?

The Mirage+ won't give you more stability, and may in fact give you less, but it will also likely go faster since your X dimension is deep. You should be pulling 5,200 to 5,400 rpms with the right prop.

What hp did you have before and what speeds were you running?

No reason that you shouldn't be able to spin the 26 faster with that HP. I spun a 24 bravo 1 to 5200 with 420hp in a 24 Outlaw.
A 25 Mirage plus will be better for top speed, but will suck out of the hole.

was running 300 hp thunderbolt at 53mph with a mirage plus 23 pitch at 4300 rpm...

we havent changed the jetting or advanced the timing yet though.. it is running a 850 HO holly double pump.. jetting is at 84 in both primary and secondary and max timing is set at 34...