somewhere on this site, at some point, I posted pics of a blowed up 351w block, which obviously is much stronger than a 302 block. However, when this engine let go it knocked the main webs out. In the pictures (which weren't great quality, I admit), you can clearly see how thin the main webs really are. Woody talked about how thin they are, and he's right. They are paper thin; and again that's a 351w block. I've knocked the mains out of a few 351w blocks, it's the weak point on those. We have to remember Ford designed them to be a lightweight casting and Henry's engineers designed them to put up with up to 300hp and what? 5500 RPM max? And we're trying to run them 7500+ with 700+hp. What do you think is going to happen at some point?
Then you compare a stock 351w block to a Dart, or even Boss block, or World block. There is no comparison, the only similarity is the pan rail location deck height and bore spacing; about everything else is better. Same goes for 8.2 based blocks. They are so vastly improved that there really is no comparison.
With that, the original question's answer. No two bolt block is going to be stronger than a production 4 bolt block because there was only one production 8.2 block (69-70 MY Boss 302 and any replacement/service blocks) and it was a different block in other ways (different alloy, etc)-so naturally it's stronger. On 9.5 deck stuff there was never a 4 bolt production 351w block, so you can't compare there either. Thus, the most common comparison is comparing an 8.2 or 9.5 deck production non-boss block to an aftermarket 4 bolt block, which as stated is no comparison.
So you're buddy who told you all this, is probably a chevy guy and you should do as woody suggested. Part ways with them. You don't need that kind of negativity in your life.
And, from my own experience the only thing the girdles do is hold the parts together when the block blows the mains out. It still self-destructs. Sometimes (and that is a key word, sometimes) they keep the rods from going through the pan rails but if you have to concern yourself with that, you have other problems to worry about.
I just thought about something else. Some of the chevyboys will often search hard for a 454 2 bolt block or sometimes a 427 2 bolt block, so that they can convert them to splayed caps. Splayed 4 bolt caps are MUCH better than inline 4 bolt caps but they still dont address the shortcomings of the stock 427 (tall deck) or 454 blocks. Thus, if guys are planning on big power and 500hp isn't that, they are almost always going to look at better parts. Besides a 454 stock block will only go about 505" and it's done, there just ain't enough block there, however aftermarket stuff can go easily 620-640". But a 460 block? I have done a couple of 557's, little to NO clearancing, they work, they run, nice cavernous crankcase. I have "read" that they'll go over 600" with a longer arm which I think exactly nobody makes as a "off-the-shelf" item. But we ain't talking about big stuff, we're talking about SBF so these are not to be considered and irrevelant