When modeling my Infinities with Qts values of .7 and .48 I noticed a noticeable drop off above 50hz with the higher Q driver. After listening to both I can confirm that. The higher Q driver had very little impact, but better low end extension. The lower Q driver has excellent impact up top and sounds much more controlled (tighter) but lacks a little on the bottom end. However compared to a sealed enclosure it is still night and day.
Mobridge DA2 > JBL MS-8 > ARC XDi 600/4 > JBL Gti 408 Mids & Vifa XT19 Tweeters; PG Ti2 1600.5 > Morel HCW-10 & IDMax 15