Let's remember that Vortech and Paxton are owned by the same company. The T-trim is a far more capable blower than the SI. Sure, the CFM rating is only 50 more, and it is rated as being less efficient, however, you need to look at the maps of the blowers and actual track times/dyno numbers. We have taken the T trim way beyond 800rwhp, where the SI runs out of steam at about 725rwhp, depending on the setup. Time and time again, we have proven the old T to still out perform the SI when being maxed out or over spinned.
The noise between the SI and T trim blowers is about the same. I've been around 90+ SI-T-YSI blowers at my shop in the last 1-2 years(turn out 2-3 cars a week). The only one that stands out as being loud, is the YSI. On the SI-T trim cars, the BOV actually is louder than the blower most of the time(turbosmart). The YSI kit on my car uses the Vortech BOV, which is quiet compared to the turbosmart or tial 50, and the blower is much louder at idle. Once in to boost, my exhaust is louder than either the SI-T-YSI, so it is hard to hear. You don't get the loud whine that a 2300 blower makes inside the car.