It's a bit simplistic to say, "やりおる is just another way of saying やる." The unmistakable nuance in やりおる is that of contempt. According to 『徳川時代言語の研究』*, there was a helping verb をる that condescends the subject of the main verb, "動詞・活用連語に附いて、動作主を卑しめ詈る意を表す" (149). The contemptuous tone of the speaker is seen in 流石と言っておこうか too. To pick a few examples from Yuzawa's oeuvre:
If you are a jidaigeki-buff, 控えおろう is also of this kind.
Now, a research** on a dialect from the Western Japan quotes a previous paper to list the characteristics of しよる (< しをる):
1. 丁寧に感じる (語調が柔らかいと感じる)
The last two are probably what やりおる is meant to convey too. The "You are pretty good" is 2. a comment on an on-going event and there is 3. an air of a first-hand observation to it. The first, 1. politeness, is somewhat out of place for analyzing やりおる, but it can be explained away by noting the self-deprecation in b., a form of contempt directed at oneself or those close to one, turning into a humble form of speech over the course of a few centuries. The overall tone of the current text is undoubtedly that of condescension as I discussed above.