The +1 holy burst is a fairly crappy weapon -- vs. a plain +5, you're trading 4 crittable damage for a 2d6 effect and the burst. The damage is slightly better than a plain +5 (total added by HB over 20 swings is 161, as opposed to 108 for the plain +5 -- a +5 of pg is up to 174.5), but the 4 additional attack bonus offsets the damage difference.
And I can't think of any way the SOS could outdamage a decent transmuter against something with DR 15+. Losing 4 glancing blows per chain at 20-25 damage each is significant. Per 20 attacks, call it +320-ish damage to a single target.