nothing like the empirical valuation of a subjective evaluation... (that doesn't really make sense, sorry I got nothing on Oscar Wilde)
hahaha, but really, Alu is fine, it'll hold out. Nearly all DH and freeride frames are made of it, yes they are built bigger, but they do 40' gaps on them too!!!
Alu frames usually have carbon forks and are usually stiffer and lighter. Most road frames are alu too. there is a comfort factor, but I think it's because people compare alu track frames to steel frames (alu track frames are really stiff). But still people ride them just fine on the street.
So in the end, **** all the stuff that people say, weight doesn't make a huge difference (unless you are going over the 13kg mark which is really unlikely in FG/SS). Just get something that fits your budget and you think looks good. Most people trade comfort and safety even for style anyway.
And don't say otherwise unless you are rocking a helmet mounted mirror!