blower rpm

I need some past experiences from others here. I have a sn93 and it is pushing 8+ psi a 4000 or so, this doesnt sound stock, is it ? Is the impeller upgraded ? I run a 6.5 crank pulley and a 3 blower pulley and rarely if even ever hit 6000 rpm, I usually shift at 5-5500 rpm . Is this a dangerous combo or will it go for a while. I know there was a post on figureing out impeller rpm , I just want to hear others experiences with higher rpm impeller speeds so i can make changes if most of you think this is a bad combo...

Formula; (crank dia/blower dia) x rpm x impeller ratio so;

(6.5/3) x 5500 x 4.4 (impeller ratio) = aprox 52K

I know speedytang rev's his up to 50K. The most i have taken mine up to was 48K. I currently need a rebuild after 3.5yrs of having mine. To see if you have the upgraded impeller, the blades have a slight curve to them. they are not straight like the standard impeller. I have the modified impeller, hope this pic helps.