Done a search, can't get a thread on this specific topic. Been a KSP player for years, like efficiency and since career mode I build for cost, every time, even if I don't need to with excess funds. I'm not bad, but not perhaps the most discerning of method in my builds.
So - using KSP Engineer and looking at how much Delta-V I can get for my buck. On build using a Swivel for a two-stage centre, I put two or four BACC SRBs on, but stage so that I launch off the pad with SRBs only. Obviously ensuring I have enough TWR for it to be viable. If I have four SRBs and enough TWR I might light only two SRBs on the pad, drop and light the next two (performing a struggling gravity turn with risk of impact when dropping) before finally lighting my Swivel.
Obviously this makes for a slow initial ascent. I understand the thick atmosphere thing at the pad, get going quickly blah blah, but when I compare Delta-V stats with Atmosphere in Engineer, doing what I say above yields more Delta-V than if I light the Swivel on the pad, or light all four SRBs on the pad if using four. Again, TWR is considered and a slower start seems to be better on final Delta-V against cost.
I'm not arguing the virtues of using SRBs at all vs liquid side-booster stages, to me that's a no-brainer on cost (I can end up with 2.5m Skipper build with no Mainsail side boosters, just six Kickback SRBs using the above method, lighting four on the pad and lighting the other two before finally lighting the Skipper, when payload makes it viable).
What I'm wondering is, am I wrong to be purely looking at Delta-V values in Engineer in these builds? What might I not be considering that is possibly making the Delta-V figures either erroneous or a bad idea for another reason I'm not considering?