Manuscript:
Well, well... This is interesting.
Take a look at Saint-Andre's translation and transcription:
Whereas other pursuits yield their fruit only to those who have practiced them to perfection, in the love and practice of wisdom knowledge is accompanied by delight; for here enjoying comes along with learning, not afterward.
ἐπὶ μὲν τῶν ἄλλων ἐπιτηδευμάτων μόλις τελειωθεῖσιν ὁ καρπὸς ἔρχεται, ἐπὶ δὲ φιλοσοφίας συντρέχει τῇ γνώσει τὸ τερπνόν· οὐ γὰρ μετὰ μάθησιν ἀπόλαυσις, ἀλλὰ ἅμα μάθησις καὶ ἀπόλαυσις.
Now, look at the manuscript...
VS27 is actually split in two in the manuscript! Those two big red Epsilons split what we know as VS27 into to pieces:
27A: Επὶ μὲν τῶν ἄλλων ἐπιτηδευμάτων · μόλις τελειωθεῖσιν ὁ καρπὸς ἔρχεται
27B. Επὶ δὲ φιλοσοφίας συντρέχει τῇ γνώσει τὸ τερπνόν · οὐ γὰρ μετὰ μάθησιν ἀπόλαυσις, ἀλλὰ ἅμα μάθησις καὶ ἀπόλαυσις.
which translates to:
27A: On the one hand, in the case of other pursuits, they yield their fruit only to those who have practiced them to perfection
27B: On the other hand, in the case of the love and practice of wisdom, knowledge (τῇ γνώσει) is accompanied by delight; for here enjoying comes along with learning, not afterward.
Note that this saying uses ἀπόλαυσις, which is the same word used in the letter to Menoikeus when talking about taking pleasure in something. Here it's a positive, in Menoikeus it's not as positive. How the same word can be used in so different ways is still beyond me for now. ἀπολαύσει, at its most basic meaning, is the “act of enjoying, fruition” or the “result of enjoying, pleasure.” This implies enjoying the benefit of something, as discussed in Menoikeus 124 and 130 with the additional meaning of “advantage got from a thing.” All those meanings are at play here in VS27.
Bailey's translation and commentary (and Cassius talks about this in the other thread in this section on VS27):
In all other occupations the fruit comes painfully after completion, but in philosophy pleasure goes hand in hand with knowledge; for enjoyment does not follow comprehension, but comprehension and enjoyment are simultaneous.
I don't see anything to justify "painfully" at least at first pass.
Again, Bailey is trying to claim a status of a higher pleasure for philosophy, a superiority.
For Diogenes of Oenoanda, it must be referring to:
Examples of coincident causes are [solid] and liquid nourishment and, in addition to these, [sexual acts:] we do not eat [food] and experience pleasure afterwards, nor do we drink wine and experience pleasure afterwards, nor do we emit semen and experience pleasure afterwards; rather the action brings about these pleasures for us immediately, without awaiting the future.
even though this is not fr. xxvi., at least in the website translation.