I agree with your machinist.
Yes splayed caps are better and are stronger. 4 bolt caps are nice to have in there. No doubt both are better.
BUT!
Back in 1984 I ran 154 mph with a 2,960 lb car using great heads and a 2 bolt Main chevy car block with two sleeved cylinders as a 461 cu in 16.85 -1 compression , and I kept it at 8,000 rpm all the time. When I was done with it after it going a 7.87 in a 2300 lb x-top fuel car I sold the short block minus cam for $500.00 and it went in a front engined alcohol dragster and he ran it several years, so it must not have been hurt. In case you have not figured it yet, that is over 1,000 hp with a stock 2 bolt block.
I would run it like your machinist suggests unless the money for the better caps is no big thing.
Ed