J/30 Class Rules paragraph 5.4.1.5 has an "Official Interpretation" annotation that states;

A list of approved replacement winches is available from the Class Measurer.

The list of approved replacement winches will be maintained on the One Design Class Rules forum and updated as necessary.

Table of Approved Winches for the J30 as of 22 August 2011

Winch	Power Ratio	Weight (lbs.)
Primaries - 2 speed
Barient 25 (Original)	44:1 and 14:1	11.9
Lewmar 43)	43:1 and 15.6:1	12.5
Lewmar 44	44:8 and 13.9:1	12.6
Lewmar 44ST	44:8 and 13.9:1	12.6
Lewmar 44STOR	44:8 and 13.9:1	10.9
Lewmar 40ST	40:2 and 13.2:1	10.7
Harken 40 or 44ST	39.9:1 and 13.5:1	11.9
Harken 46 or 46ST	46:5 and 11.7:1	17.2
Harken 42.2	42:1 and 14.2:1	13.6
Harken 44.2ST	44:1 and 13.8:1
Secondary – 2 speed
Barient 21 (Original)	30:1 and 7.1	9.3
Lewmar 30	30:1 and 7:1	6.4
Harken 32.2	32:1 and 6.8:1	7.3
Halyard – 1 speed
Barient 10 (Original)	7.6:1	3.7
Lewmar 8	7.9:1	3.09
Harken B8	7.5:1	2.31

The table is available to download and print via the attached Word document.

The Lewmar 40ST has been added to the approved list for primary winches

I don't see a Lewmar 44ST winch listed on the manufacturer's website. Did you mean the Lewmar evo45ST?

with all the new models that have been introduced I will update the list The evo 45 will probably fall in with it

comparative data
Approved:
Lewmar 44ST 44:8 and 13.9:1 12.6
Lewmar 44STOR 44:8 and 13.9:1 10.9
New:
Lewmar 45ST Evo 44.8:1 and 13.9:1 7.2kg (Black/Grey Alloy)
Lewmar 45ST Evo 44.8:1 and 13.9:1 9.7kg (Chrome Bronze)

the Lewmar 40ST would be a replacement for the secondary and not the primary winches, if considering Lewmar: the hole pattern for the Lewmar EVO 45ST does not match the Barient25; the "Fast Fit" idea was never implemented, no studs supplied. Winches are mounted in the conventional manner.

The 40's are not approved for use as a secondary they are two large Power ratio's are to high