Only a few UV-emitting species has been employed in TTA-UC to date, with 2,5diphenyloxazole (PPO) arguably gaining the most attention. Pioneering work by the Castellano group dating back to 2009 employed PPO together with biacetyl, albeit with very low efficiencies. It is only as of 2021 that a system employing PPO surpassed 10% in FUC, which was achieved by pairing PPO with a cadmium sulfide nanocrystal sensitizer decorated with 3phenanthrene carboxylic acid. The 10% limit has also been surpassed by pairing an iridium complex or a ketocoumarin derivative with 1,4-bis((triisopropylsilyl)ethynyl)naphthalene (TIPS-Naph), systems which also demonstrate low threshold excitation intensities (Ith). Other annihilators previously investigated include other naphthalene and oxazole derivatives, species from the terphenyl family, and as of recently also a biphenyl derivative with the capability of emitting light beyond 4 eV. The spin-statistical factor, f, gives the probability that an excited annihilator triplet state ultimately ends up as a singlet excited state following TTA. In annihilator species in which the second triplet excited state (T2) is energetically accessible during TTA, f takes the value of 2/5 for strongly exchange-coupled triplet pairs, which caps FUC to 20%. Annihilators yielding significantly higher FUC, such as a few based on perylene, have been shown to have f » 1 since T2 has too high energy to be populated following TTA. This classical way of approaching the spin-statistical factor has recently been questioned, suggesting that a broader range of values could be achieved and which depends on e.g., the nature of the initially formed triplet pair states. In this study, we aim to shine light on the fundamental aspects currently limiting vis-to-UV TTA-UC. A thorough and systematic investigation of both known, relatively efficient, annihilator species as well as two compounds that has not been used in this context previously has been performed. The six annihilators used here are paired with a high triplet energy thermally activated delayed fluorescence-type (TADF) sensitizer, allowing for efficient population of also highly energetic annihilator triplet states. We show that also vis-to-UV TTA-UC systems may approach the spin-statistical limit of 20%. Specifically, employing TIPS-Naph as the annihilator species yields a record-setting FUC of 16.8% (out of a 50% maximum), which is an almost 2-fold improvement on the previously best-performing vis-to-UV TTA-UC systems. High FUC are also obtained for PPO (14.0%), 2,5-diphenylfuran (PPF, 13.0%), a compound never used for vis-to-UV TTA-UC before, and for p-terphenyl (TP, 12.6%), a compound which emits much deeper in the UV. The performance of the remaining systems are also evaluated and the intrinsic properties governing the TTA-UC process are obtained and analyzed. Further, we discuss what implications these findings have and what obstacles still need to be overcome in order to improve these systems for future application in photochemical settings.