If you have the budget to go 18 degree, or even less degree... That would be good but I don't think it's needed in a street car with the cam you're running. You'll never see the full potential. Plus, you'll need shaft rockers, off-set lifters, matching pistons, etc...
If this was a high rpm, (8000+) high compression, (15:1+) huge roller cammed engine, (280 @.050"+) I'd say you needed 18 degree or better heads...
Brodix make an 18X degree head that uses standard valve train but it doesn't flow but what the CNC 220cc 23 degree head flows.
Just my opinion...