as per the title really, whats the main differences and will I notice anything (I think I already know the answer to this one given my riding ability!)
6061 requires heat treatment after welding, 7005 doesnt. Due to the mix of the alloy.
is heat treatment good or bad? characteristics the same? is one lighter?
if heat treating was bad then it wouldn't be needed
I don't think anybody would notice the riding difference between 6061 and 7075!!!
The answer is no, you will not notice any different in the metals, though the two frames could chalk and cheese.
very very few designers/manufacturers actually build to the strengths of the tubeset, ie using a little more ductile temper in the seatstays as opposed to the frotn triangle.
Something like Kleins Zr1 was the last true 'bike aluminium'
6061 IS better (stronger), but more expensive and harder to heat treat.
7005-t6 - 290 MPa yield
6061-t6 - 276 MPa yield
according to matweb