Long ago, my first L lens was an oddity: the 300 f4 L. Hit with the ladies. Bought for $400, sold for $720 on eBay. Missing it dearly (even though I never used it) I found a 300 f4 L IS for $660 on eBay, with a 1 inch mark on the front element.
Used it for indoor sports (mostly cheerleading) in the university's gym. But it had few rentals. So I put it on the chopping block.
Last night I ended up trading my $660 investment for a Sigma 24-70 f2.8 IF HSM and $120. Not L sharp at f2.8 on the 6D, but I like the color. Also handles better than the 24-70 L imo.
Good deal or not? Should I sell and add cash for a 28-70 f2.8 L that will have better f2.8 performance AND be more rentable? Old model or not, renters looooove the red ring!