Banchetta, in the term "decking the cylinder" are you referring to lowering the cylinder itself or just referring to the spacer on the top? Although the options are endless in setting up a +4, it has been my experience that they love transfer duration and if you give it enough of it, you can go with some pretty wild exhaust durations as well and still have killer bottom end and only give up a few hundred rpm on the big end compared to a heavily ported 350 crank motor.. Even with the loss of peak rpm, the motor will still pull much harder and longer even with tall gears so your top-end speed is still WAY improved over a radical ported 350 crank and still have killer bottom end.
If your goal was low -end, and I'm just assuming that it is, it might be that your engine is wanting more transfer duration depending on how you "decked" it. If you give it enough transfer duration, 200 degrees ex. duration is not excessive and still have major grunt...Jim