Not got much experience of SLX but people seem to like it 🙂
The only real issue, apart from a little bit of weight, is how you are going to use the bike.
If you are going to be hardcore riding all year round through mud etc then I found that kit below XT level would wear out, whereas when you get to XT level it tends to fair better. But I was quite abusive with the amount of mud I used to ride through (70+ miles a weekend on the north downs al year round whatever the weather).
So you should still put the frame and forks first, but try different bikes if you can as the geometry/fit will make a big difference.
For instance I had a 19inch Kona Muni Mula to start with, then changed it for an 18inch Kona Explosif for better fit and to get away from harsh aluminium, and then to the Wanga for a nicer fit with 100mm forks.
Some bikes are stretched out, some are compact. Some have a steeper head angle and therefore the steering is sharper and more to your taste, or you may want the slower reaction from a longer travel bike which goes downhill better. Stem length can also make a big difference.
And if it turns out you don’t like the ride of your new bike then, as long as it is pretty standard and doesn’t use fancy integrated headsets and stuff, you can swap the frame out for a 2nd hand frame from ebay – thats where my explosif and wanga frames came from.If you have a reasonably sought after frame in the first place (wanga?) then you should be able to sell it for a reasonable sum – when I sold the explosif I made a profit on it 🙂
Are you anywhere near junction 11 of the M25, you could have a whizz on my Wanga if you are.