Just to go back to the OP's question - I think the real answer is: It depends.
I have a real outlier - a 76 43' Viking Double Cabin - identical hull to their sportfisherman - just infilled the SF cockpit to make a stateroom. Power is twin 454 Crusaders rated at 350 hb - carbeurated with electronic ignition. The Hobbs show about 1650 hours. I have no objective history on the engines other than knowing through serial numbers that the blocks and heads are time commensurate with the build date for the boat. Original? Repowered with correct vintage remans? Rebuilt in place? Dunno.
Viking produced a couple of hundred over the period of 76 to 83 (?) or so. They were optioned with either the Crusaders or 6-71s. Talking to the Viking guys over the years (including Paul, who project managed the DCs but has since retired) it seems they were about 50/50 diesel/gas. But no hard records.
I do know that the old girl will still make the Viking advertised numbers for speed (27 K) and that the oil analysis results for the past 4 years is good and stable. Compression is good all holes.
Normal operation is either in "trawler" mode at about 8.5 - 9 K (2200 rpm, 8 gph by Floquips) or (if I'm feeling flush that day) a planing sweet spot of 13.5 - 14.0 K (3200rpm).
Am I worried about the safety factor of gas? Yes, to the extent that I take precautions, have systems that help to manage that risk, and conduct preventative maintenance - just like I did/do with aircraft that I flew, other smaller boats, cars that I drive, and the myriad generators, power washers, lawn mowers that I own. I'm by no means a wrench-head, but upkeep is pretty straightforward with basic handtools.
I'm pretty much a day cruiser, with occasional expeditions to the barrier islands off AL and MS or a run to the Florida panhandle. She's good for 150-200 miles with reasonable reserves. Fuel economy? In my experience, and doing maybe 200-250 hours underway per year, the cost of fuel is one of the less expensive items in boat ownership.
When I bought her (yes I had her surveyed by an old established surveyor who knows old boats), everything was sound - but not pretty. I talked to a lot of guys who operate 454 powered work boats (lafitte skiffs, mostly - working small operation fisherman) who swear by the big block Crusaders. last a long time, easy to maintain, relatively inexpensive to replace/rebuild when compared to a lot of diesels. Decided that, net out, for that boat and my intended use - she worked. And never looked back.
If I were one of you guys in the PNW who runs up to Alaska now and then, I'd have never considered her. If I had believed everything I read about the 35' or 40' "cutoff" for gassers I wouldn't have bought her. But for my deal, the gas power works out perfectly. I don't have a shred of diesel envy.