In RV IV.57.6, the word sītā means furrow and in RV X.93.14, Rāma is either a reference to a psychological power or a rich prince at the time (not Rāma Dāśarathi).
From R. L. Kashyap's translation and notes on those RV verses:
4.57.5: May shuna and sīra be pleased by this our praise (1). May they sprinkle this (earth) with the bliss (3), which you have created in
[shuna-sīrau: The two indicate the forces of prāṇa (Vāyu) and of mind
(Indra) which should be in full accord in all conscious work; ancient
authorities interpret the two in different ways: Vayu-Sun (Yaska),
Indra-Vayu (Shaunaka), Vāyu (Ashvalāyana), Indra and Surya
The physical meanings are: sīra: plough, plow; shuna: plough-share
(or plow-share), a part of the plough that cuts the furrow; Note that
S regards sīrā as 'rivers' in (4.19.8).]
4.57.6: Blissful sītā, be present, we offer our obeisance to you (1).
May you may be felicitous to us (2). May you yield us abundant results
(or fruits) (3).
[sītā: the furrow, symbolic of action;]
4.57.7: May Indra take hold of sītā (1). May Pushan guide her (2). May
she, well stored with bliss, yield us the milk of knowledge, year after
[This is in Atharva Veda (3.17.4)]
10.93.14: In the presence of Duṣhīma, Pṛthavāne, Vene (1),
the mighty Rāma and the opulent princes, I proclaim this (2).
Having yoked five hundred horses (3),
their affection for us on the road is celebrated (4).
[The names such as Duṣhīma etc., in (14) and (15) refer to certain psychological powers. Any explanation given can only be a conjecture.]
From The Society of the Ramayana (by Ananda W. P. Guruge) which takes a more historical approach:
§ 13. Rāma which in the Ṛgveda X, 93, 14 is the name of a rich sacrificer bears no semblance to the hero of the story. Sītā, likewise, in Ṛgveda IV, 57, 6 and 7 is the "furrow" and even when addressed as "auspicious Sītā, come thou near: we venerate and worship thee" it is only a personification of the furrow or agriculture. Nevertheless, the story of Sītā's birth narrated in the Rāmāyaṇa indicates that Sītā's association with the furrow is to some extent preserved. Lakṣmaṇa, in its patronymic form Lakṣmaṇya only indicates that it is a very old proper name.