I've "faced" this issue... My comments:
1) It's rare. If these things regularly caused oil starvation, they wouldn't be sold.

2) I think it might be a problem on some motors that have high valve spring pressures - motors that really need the oiling capacity up top.

3) These things HAVE to reduce oil flow somewhat - if you compare the diameter of the stock bolts (tapered) with an ARP, the ARP is larger, it's larger right smack dab in the middle of the oil supply portion of the head.

For 98% of motors, I don't think it matters... I think it might matter if you have high valve spring pressures, a head casting that has a reduced or otherwise different from OEM oil passage design, and maybe some unknown 3rd factor.

I can tell you that I had a top end oiling issue at one time. I did two things to resolve it in combination - so I can't tell you what the "fix" was - so I'm suspicious of both things:
1) reduced valve spring pressure to something reasonable, I think under 190PSI at .450 lift, if I recall right - check with Ted, he won't steer you wrong in regard to valve spring pressure.
2) Removed the #1 cylinder passenger side ARP and went back "stock" bolt. This is where the oil feed for the head comes from.


For anyone curious, you can see the taper on a stock head bolt vs an untapered ARP here:
http://lakebox.dnsalias.com/photos/1988%204runner/engine/rebuild/arpvsoem.JPG

Note, I highly recommend ARPs due to the HG issues with these motors...