Hmmm that was my exact thought joe, a wishbone's a wishbone surely but when it comes to bushes I guess there could be a lot of difference. Having said that though, what's to say that they won't be the exact same bushes that are fitted to the gsf wishbones, after all they are all pattern parts. I just priced the gsf stuff up and if you buy the wishbones and bushes separately it comes to £25.50 (without bottom balljoint though), it's only when you buy the wishbone with the bushes ready fitted that it suddenly goes upto £37.60
I suppose I could buy the cheaper ebay ones and if the bushes turn out to be sh!te I could upgrade to some poly ones at a later date. I'm planning to fit eibach arbs with poly bushes at some point this year anyway.
Tough decision without having either of the parts in your hand to compare them!!!