No, a 5W-30 can be less viscous than a 0W-40 at say -10C. Wax crystal formation in non-PAO primary bases (so excluding esters and AN's, which tend to be co-bases) is pushed to lower temperatures via the use of PPD's (pour point depressants), as it is those wax crystals that ultimately drive the massive increase in viscosity and gelation that's experienced with Group I/II/III bases at low temperatures (this is not experienced by PAO). So a Group III based 5W-30 could be 300cSt at say -10C and a 0W-40 600cSt, but the 5W-30 starts to run into the limits of its PPD's at -32C (CCS for a 5W-xx is measured at -30C) and it barely passes MRV at -35C, while the 0W-40, which has some PAO in the base oil blend, easily passes below the 6,200cP limit for CCS at -35C.
There's no concern about "flow" at the temperatures at which we are discussing here, we aren't talking about oil that is 10's of thousands of cp putting the oil pump on the pressure relief and potentially restricting how much oil is flowing through the engine until it warms and viscosity reduces a bit. So yes, there's no reason for concern about wear, these are temperatures easily handled by a 10W-xx.
Full-SAPS oils aren't restricted on, well, SAPS, which includes a few chemicals, like phosphorous, that help with anti-wear. A lot of effort goes into making oils that are restricted by the mid and low SAPS envelope perform at the level the approvals these oils carry mandate. Mobil 1 ESP oils are a good example here, which often have phosphorous (the primary AW component of the ZDDP compound) close to or right at the 900ppm upper limit, while FS 0W-40 carries 1,000ppm.
The ESP oils are designed to be kind to exhaust aftertreatment devices like DPF's and GPF's, while the full-SAPS oils (eg, A3/B4) are not.
