I was running just about as much boost as I could get short of wiring the waste gate closed. I would start out at about 28-29 lbs, but it would drop off after 4900-5000 rpm. by the traps I was 23-24 around 5300-5400 rpm. The biggest changes left to make would have been a better intercooler and taller tire from what I could tell.low boost?hmmm,i drove one with just a ported head it went 11.5 on 20 psi had 28/32 degrees of timing though.
I picked up the 5858 used NIB for a decent price so I figured why not. I don't race, just test and tune, just like to play with the car. So in that context, I think the 5858 is decent upgrade over the 44. If I wanted a solid 10 second car I would have went straight to a 6262.
Back to the OP, if he is only looking to get rid of the surge, the 5858 is an option.
The exhaust housing change is an interesting option. While it doesn't seem to make a difference for peak performance for the 44/49, it has to make a difference at part throttle flow to cure the surge.