On pg. 101 in discussing the outcome of *ei, I failed to mention some additional evidence that bears on the question. The mid-stage between *ei and ī is thought to have been a high mid [e:]. This stage is attested in forms from some archaic non-Roman inscriptions like VECUS (ILLRP 267, Castelluccio di Lecce), VECOS (ILLRP 286, Trasacco), VECI (ILLRP 303, ad Lacum Fucinum), VEQO (ILLRP 1217, Cales). But Varro mentions two instances where the rustic pronunciation still in his day substituted an e for and urban Latin ī.
Varro R.R. 1.2.14:
A quo rustici etiam nunc quoque viam veham appellant propter vecturas et vellam, non villam, quo vehunt et unde vehunt.
And for this reason even now they rustics call the road veham because of the acts of conveyances and the farmhouse vellam, because they convey things to and from there.
Varro R.R. 1.48.2:
Spica autem, quam rustici, ut acceperunt antiquitus, vocant specam, a spe videtur nominata.
Buts spica which the country people continuing an ancient tradition call speca is so-called because of spes 'hope'.
These two forms speca and vella are generally thought to reflect the pronunciation of dialects where the diphthong *ei merged with ē rather than merging ultimately with ī as happened at Rome. In the case of vīlla/vēlla, there is no doubt that the immediate preform was *weilla, but in the case of spēca this is not quite so certain. The root of Lat. spīca is connected with that of spīna 'thorn'. The latter word is apparently cognate with Umb. spin(i)a 'obelisk' vel. sim. The consistent spelling with i in Umbrian (II a 33, 36, 37, 38) points to an ī, which cannot be the result of the monophthongization of *ei. If so, this suggests the root in question is *sp(e)ihx-, which would not have had given a form *speikā.
The Romance evidence sometimes seems to continue a non-urban monophthongization as in Sp. Port. Cat. esteva, OFr. estoive, Ital. stev-ola/steg-ola which continue a non-urban *stēva not stīva 'shaft of a plough-handle'.
On the other hand AMECIS (CIL 4.3152a, cf. Paul. ex Festo p. 15L: ab antiquis... ameci et amecae per e litteram efferebantur) may reflect a hyper-non-urban pronunciation since the suffix -īko- is usually thought to continue an original long vowel.