Welcome Beezer, While I haven't been directly involved in the chain conversion or done one yet, I do own both an old 87 model 4-speed and a 99 model 5-speed. So, I'm very familiar with the gearing feel and shift points of both types. I think that will give me perspective to help you out. Also, I weigh over 250 all by myself, so I load a bike almost as much as your 2-up situation.
I'd have to say that I would be reluctant to gear the old 4-speed any higher than stock, unless I was much lighter, and planned on riding the highway at 65-70+ a LOT. One of the main reasons being that the 4-speed has a bit of a tall first gear to start with, and making it significantly higher would be hard on the clutch.
And OTOH, If you want to maintain the ability to cruise at 65-70 for any length of time, you certainly don't want to gear the bike down any; because it is already geared barely high enough to cruise at those speeds as stock.
So what I highly recommend is to continue to ride the bike geared just as it is with the belt, unless you have some serious shortcoming in the performance or suitability for the type of riding you do. Only when and if you decide that the bike is being worked too hard on the highway, or you need more pull because you live in a hilly area; THEN... MAYBE you might want to look at the chain conversion. Remember, that you can get a slight gearing change by changing rear tire size/profile.
Frankly, I'd recommend that anyone planning to use a Savage for a lot of 2-up riding, consider trading up for a 5-speed model. While the top gear is only very slightly taller (when the difference in primary gears is considered)... First gear is noticeably lower, and the other gears are spread at very handy intervals for a variety of in town and road riding.
In fact, I've been thinking about the best use for my old 4-speed Savage. I've wanted to have several of the bikes, each converted for different uses. I don't see the 4-speed as good potential for a scrambler type bike; because of it's lack of wide enough gear ratios. The same goes for it being any other type of bike that needs a really wide choice of gear ratio. So... I'm thinking it would be put to best use as either a very high geared solo highway bike, where taking off in a really tall first gear wouldn't matter much. Or, perhaps a cafe' style bike with the gearing set to really pull in the 15-65mph range where I enjoy peg dragging most. I'm not much for really high speed road racing style riding. I am quite capable of scaring myself plenty enough below 70mph thank you
As it happens, the bike pulls great in that speed range with the belt that is already on it... so no need to change anything if I were to cafe' it!
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