Well, I have both. the only problem I have had with the 6008 is well, 2) really, is 1) the batteries go out in a flash of time so, I rebuilt them and now they are fine... about $35 each... great camera, leading to problemo 2) which is that it is a cinder block of a camera... heavy and bulky, but with that 80mm Planar it cannot be beat.... No, Sir.
The SLX uses the same PLANAR, making that a wash. The meter on the SLX is a bit clunky but works well. batteries are a problem but easily rebuilt. Good camera as well. The only push is the price. So, get the SLX and get used to it and see if the features of a 6006 or 6008 are what you need and jump that way keeping the SLX as back-up. That's what I did. Oh, and I got two SL66's into the bargain which I like even better.
Logan