Surely the most important thing here is to check the precise wording of the entry packs for any recent GW tournaments regarding proxy models and if there is any uncertainty, contact GW?
For what it's worth, one of the reasons I avoid 'official' tournament play like the plague is because I cannot stand being dictated to about how I enjoy my hobby and how I use my models....but then I am a grumpy old blighter
As you'll see if you follow my WIP about my Elves, I don't think one single model is actually being used for what it was originally intended. Obviously you won't see me at a tourney any time soon, but you may rest assured that I and my gaming buddies who play with me, will have hours of endless fun playing and I will certainly have hours of fun painting and converting the models.
At the end of the day, it's all about how you wish to play the hobby. If you wish to do the official tourney circuit, buy the right models and play the GW game, or do 'proper' conversions where it's appropriate. If not, agree with your mates what is acceptable and what isn't and just have FUN
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For more of my painting and gaming stuff, please visit my blog:
http://guitarheroandy.blogspot.co.uk/Thank you