I am not running a sniper EFI, I'm running a modified Howell GM TBI system, but I personally found that vacuum controlled EGR function can wreak havoc with the tune. Since the Howell system (inexplicably
) doesn't use the ECU to control the EGR, the ECU doesn't know whether or not the EGR is on and thus, can't compensate by commanding less fuel to the engine. I found that reducing the orifice washer in the EGR helped, and also adding a vacuum delay valve, but eventually just ended up disconnecting it for the time being.
I think that EGR is a good thing to have though if properly tuned. More than anything it will improve your gas milage at light throttle and cruise by introducing inert gas allowing the mixture to use less fuel and reduce pumping losses because it will require more throttle opening to maintain speed. I wouldn't be worried too much about high combustion temps at cruise (though EGR will lower them), and EGR is not active at idle so there won't be any effect there.
I plan on wiring it up with a solenoid to control it (just as the full GM system does) in the near future. I'd also like to do timing control at the same time. I've just been lazy and busy with other projects.