We managed to get hold of a pair of discontinued Gibb winches when they were taken over by Lewmar. They are 52s, on a Sadler 34 and we paid less than the price of a pair of Lewmar 40s for them. Our genoa is fairly large, so the winches are fine until just before it is time to reef, when sheeting in after tacking becomes fairly strenuous for me and completely impossible for my wife.
If you take a look at www.classicmarine.co.uk, they list winches from a Dutch company called LVJ, including 2-speed and ST, which are competitively priced and may be worth considering. They also include size recommendations, which you can also find on places like Lewmar's web site.
It depends, to some extent, upon the size of your foresail/genoa; as noted in other replies manufacturers provide guidence normally in the form of a table; you will also find such a table in the Cruisermart catalogue. Both my wife and I find Lewmar 43's satisfactory on our 37 foot sloop. The area of our genoa is 360 square feet. Hope this helps.
Why not look at the Harken web site. They have a free access programme which you input the class of your yacht and if it is on their database you get a listing of recomended winch sizes and control line configuration for both cruising and racing use.
It is a fairly comprehensive database as I was able to download all the data on my Contention 33 although it did not even get a passing mention in the YM A-Z of yachts.