I get what you're saying for sure Ron. A little extra depth is a plus in some situations.
Like you, I re-entered the hobby at about the same time (2010). I recall in all the Forums, at that time, the "mine is deeper than yours" discussions between brand/model owners.
I have personally found that, the vast majority of my quality finds with any of my detectors, are well within, and mostly, far less than the maximum depth capabilities of those machines with nothing more than an 11" DD coil, including my CTX (which has the 17" coil available), or my F75 gold. I don't have any coils larger than an 11", simply because I didn't see the necessity for additional depth. The boost process, while giving a bit more depth without a larger coil, comes at a pretty steep price, at current pricing.
For my purposes, I simply looked at the cost/benefit factor for my detecting preferences. The current F75 gold, with all the upgrades, I view as a tremendous value. With the included 15" coil, even more so! I just didn't see the value/benefit of paying $500 more to have the boost process in the F75 Ltd at current prices. Prior to the current price drop, the price differential between the standard F75 and Ltd with boost, was only a couple hundred dollars, which was a bit more reasonable, from a comparison standpoint IMO.
I guess that's where my comment about it depending on the preferences of the purchaser apply. I find that I prefer good separation/ID at up to 10" of depth, as that is where the overwhelming majority of my finds are. The F75 gold with it's 11" DD coil gives me that, and more, very adequately. I guess IF I were looking for more depth I would buy a larger coil for less than $200 and take my chances, I don't see the need to do so, for my purposes anyway.
That's the nice thing about having the choices in different models/features. One of those models will provide at least most of the preferred features for prospective purchasers to serve their needs.
I agree that the F5 is indeed a nice machine! A very good and unique set of controls and user information! I wish all machines had a ground phase value, and ground balance value readout to monitor changing conditions!