My cousin had the XE 284 in a 355 with just over 10:1 comp, rpm intake and a 650dp. It definitely sounded wicked. In my opinion, it was a little much. He had some fuelie heads with a bit of work, and the drivetrain was right, but all in all, I think it coulda used a lot more head and more like 11:1 comp. It was in a 68 chevelle that ran mid to low 13's with descent traction, which didnt impress a whole lot cause I know others with virtually identical setups in similar weight cars, but with a smaller XE 274 cam and better heads running close to 13 flat. One of the cars was a late 80's monte carlo with a 355 chev, same 4.10 gears and 3500 converter, but with dart 200cc iron eagles and the 274 cam and it was a few tenths faster than my cousins chevelle....the monty ran right around 13.0's. The tuneup on the chevelle was messed with a lot too and it did hook well, so I attribute the lack of performance to a bit of a mismatched engine combo moreso than anything else that might not have been optimal. It probably would have run just the same with a 274....the bigger cam was overkill for the top end of this particular engine.
Later down the road my cousin swapped on performer rpm heads and started busting high 12's. On average it was about a half second faster than it was before, so the fuelie heads must not have been very well done....or they really are just that much less of a head. I figure with a single plane intake, close to a point more comp, and a 750 carb, that cam would have been better matched and should have been in the mid 12's or faster.
If you use the 284 camshaft in a 350, I would want no less than 10.5:1 comp and it could benefit with about a 200cc head and a single plane(dual plane will work, but single plane is better suited if you want max effort) with a 750dp and of course a solid drivetrain similar to what that chevelle had. And, it will sound rather radical.
If you want my honest opinion, that cam doesnt have much business being a hydraulic cam. I mean, its got 240 degrees duration at .050 and is intended to run to 6500+rpm. At this level, a solid would be better suited cause the solid lifter valvetrain will be more apt to perform better at such high rpm's. A hydraulic cam at 6500rpm or more is beginning to become a crutch. Not that it will be slow cause its such a big cam.....low 12's isnt slow and I beleive that this cam can run that fast in a properly set up 350, but a solid would be easier to do it with. I guess I should re-state what I said. That cam would be a nice match for a larger displacement small block. That way, depending on the size of the engine, it could make all of its power below 6500rpm and thats ok with me. But those kinda cam specs in a smaller 350 would be better off on a solid camshaft cause of the kind of rpms you have to turn to use all the cams power. A lot of that is just my opinion(cause I like solids for high rpm small blocks)....its not definite fact. If we are talking about a 350 inch motor, my own personal rule says that if I need more than 236 degrees duration at .050, than its probably time to go with a solid. An XE 274 cam with about 10.25:1 comp and 1.6 rockers would have a nice racey, mild rough sound to it. See if you can find anybody with sound clips of any of the cams you are interested in with a similar engine set up. You can get an idea of the idle sound from that.....and performance can be very good for both of them, so its up to you in the end.