The SBP is the better driver. However they model virtually on top of each other. You cannot get the IB an longer and the SBP is the replacement, so look no further. The QTc of around 0.6 is perfect IMO. I tried QTc of .7 and higher and I did not like it, too loose sounding.
Mobridge DA2 > JBL MS-8 > ARC XDi 600/4 > JBL Gti 408 Mids & Vifa OT19 Tweeters; PG Ti2 1600.5 > Morel HCW-10 & IDMax 15