<p>The 24L II is a specialty lens but I find its probably my most used lens since I use it on crop and full frame ( thanks William W ) along with the 135L ( I too love primes ). I've thought about replacing it with a 24-70 2.8 II but I ended up getting the F4IS version since I could not justify keeping the primes with the 2.8 II and I usually fall back on primes. I've owned the 24-105 and 24-70 2.8 I and I've never really needed or liked a standard zoom. The F4 IS had me curious because of the macro and small size so I picked one up recently. </p>
<p>I feel your pain as I would find it hard to part with any of my main primes ( 24LII, 50L and 135L )</p>
<p>How long have the 24/35 been sitting? I would have a hard time justifying both the L primes with the 24-70 2.8 II. Since you seem to prefer the 24-70 I would say sell them or at least the 24. 35 is very practical and the 35 is dropping in value so its probably worth keeping.</p>